The invention relates to improvements in friction clutches, especially for use in motor vehicles. More particularly, the invention relates to improvements in friction clutches wherein a pressure plate is non-rotatably connected to a rotary housing so that it can perform limited axial movements relative to the housing, and wherein a clutch disc or clutch plate can be clamped between the pressure plate and a counterpressure plate (such as a flywheel) under the action of a diaphragm spring which bears against the pressure plate in the engaged condition of the friction clutch. The diaphragm spring is axially stressed between the pressure plate and the housing and is tiltable relative to a seat which is carried by the housing. The friction clutch further employs an adjusting unit which compensates for wear upon the friction linings of the clutch disc.
Automatic compensating devices which ensure that the pressure plate is acted upon by the diaphragm spring with a substantially constant force are disclosed, for example, in published German patent applications Serial Nos. 29 16 755 and 35 18 781. These compensating devices are adjustable in response to signals from a sensor and are disposed or operate between the pressure plate and the diaphragm spring. The pressure plate is coupled to the housing by tangentially extending leaf springs which must be designed to exert a relatively small force because such force opposes the bias of the diaphragm spring. Therefore, when the friction clutch is disengaged, the pressure plate (whose mass is rather substantial) is likely to perform axial reciprocatory movements which involve repeated stray movements into and out of contact with the diaphragm spring. This not only adversely influences the operation of the friction clutch, but can actually cause the friction clutch to become a safety risk because the compensating device is being adjusted in the disengaged condition of the friction clutch until the pressure plate comes into contact with the clutch disc, i.e., when it is no longer possible to disengage the friction clutch. Therefore, compensating devices which are disclosed in the aforediscussed published German patent applications failed to gain acceptance by the makers of friction clutches.
Presently known proposals to compensate for wear upon the friction linings of a friction clutch are further disclosed, for example, in German Pat. No. 29 20 932. According to that patent an axially movable adjusting device is installed is or can be effected by wedges which bear against the pressure plate and can move the adjusting device toward the diaphragm spring in response to angular displacement of the adjusting device relative to the pressure plate. It is also proposed in that patent to change the positions of the wedges for the purpose of moving the adjusting device relative to the pressure plate.
The means for ascertaining the extent of wear upon the friction linings in conventional friction clutches of the above-outlined character comprises a plurality of sensors which operate between the pressure plate and the counterpressure plate (normally a flywheel) or between the pressure plate and the cover. When the clutch is engaged, the sensors are displaced by a distance depending on the extent of wear upon the friction linings, and the extent of movement of the pressure plate away from the counterpressure plate in response to disengagement of the clutch is altered depending on the extent of adjustment of the sensors. The operation of conventional automatic wear compensating systems is based on the assumption that, when the friction clutch is new, the disengagement involves a movement of the pressure plate (away from the counterpressure plate) which exactly matches the extent of movement of the diaphragm spring. When the friction linings undergo a certain amount of wear, the pressure plate moves toward the counterpressure plate (flywheel) through a distance which is dependent on the extent of wear. Therefore, in the absence of any undertakings to the contrary, the diaphragm spring is then required to cover a greater distance from the cover toward the counterpressure plate in order to bias the pressure plate against the adjacent friction linings, i.e., to clamp the friction linings of the clutch disc between the pressure plate and the counterpressure plate. In other words, the distance which is covered by the diaphragm spring then exceeds the distance covered by the pressure plate. This results in appropriate axial displacement of the adjusting device in a direction toward the diaphragm spring.
A drawback of the conventional proposals is that the adjustment does not always correspond to the extent of wear upon the friction linings. The reason is that the extent of movement of the diaphragm spring in response to engagement or disengagement of the friction clutch fluctuates within a certain range, even if the extent of movement to disengage or engage the friction clutch is constant. The bearing or bearings which form part of the disengaging means and serve to displace the customary prongs of the diaphragm spring during disengagement of the friction clutch are particularly likely to perform movements which depart from the expected or prescribed movements within a rather wide range. Furthermore, when the clutch disengaging mechanism (e.g., a mechanical disengaging system) is adjusted, its actual adjustment is likely to depart from an optimal adjustment, for example, because the clearance between the disengaging system and the diaphragm spring is too small and/or because the initially selected stress between the disengaging system and the diaphragm spring is too pronounced. This results in the establishment of operating points which depart from the optimal operating point of the friction clutch.
If a friction clutch is equipped with an automatically adjustable disengaging system e.g., with a hydraulic system which employs a master cylinder and a slave cylinder, the aforediscussed means which is to compensate for wear upon the friction linings cannot be operated at all because the extent of movement to disengage the friction clutch is the same during the entire useful life of the clutch. Thus, no adjustment will take place as long as the movement of the diaphragm spring in the region of the adjusting device during disengagement of the friction clutch is less than or at most matches the extent of movement of the pressure plate. On the other hand, if the extent of movement of the diaphragm spring exceeds the extent of movement of the pressure plate, the adjusting device is actuated and carries out an adjustment during each disengagement of the friction clutch irrespective of the extent of wear (or any wear) upon the friction linings so that the friction clutch is totally misadjusted after a relatively small number of disengagements.
An additional problem which arises in conventional self-adjusting friction clutches (i.e., in clutches wherein the relative positions of the pressure plate and the diaphragm spring are to be automatically changed as the wear upon the friction linings progresses) is that the pressure plate is likely to become disengaged from the diaphragm spring in the axial direction of the clutch in response to characteristic resonant vibrations. This results in the activation of the adjusting device which induces a total misadjustment of the friction clutch and renders it useless for its intended purpose.
Friction clutches of the above-outlined character are further disclosed in published German patent application Serial No. 24 60 963, in German Pat. No. 24 41 141, in German Pat. No. 898 531 and in German Auslegeschrift No. 1 267 916.
A clutch assembly has a friction clutch comprising a pressure plate which is non-rotatably connectable with a counterpressure plate for limited axial movement with respect thereto, and at least one biasing spring provided to urge the pressure plate toward a clutch disc which can be clamped between the pressure plate and the counterpressure plate. There is further provided an adjusting device to compensate at least for the wear upon the friction linings of the clutch disc so as to effect a substantially unchanged application of force by the biasing spring to the pressure plate. The friction clutch further comprises actuating means for engaging and disengaging the clutch. The actuating means is operable by a disengaging member which is shiftable axially by a disengaging means, e.g., a disengaging fork which is pivotably mounted on a transmission case.
A clutch assembly which is constructed and which is operable in the aforedescribed manner is known, for example, from the published French patent application No. 2 582 363. The actuating means of such clutch assemblies can be acted upon by disengaging systems, or by disengaging means and a disengaging member in a manner as disclosed, for example, U.S. Pat. Nos. 4,368,810, 4,326,617, the published German patent application No. 27 52 904 and the published German patent application No. 27 01 999.
Clutch assemblies or friction clutches utilizing an integrated adjusting device which compensates at least for the wear upon the friction linings of the clutch disc exhibit the drawback that, especially when employing so-called mechanical disengaging systems wherein the movements of the clutch pedal are transmitted to the actuating means of the friction clutch by way of a linkage and/or a Bowden wire with the interposition of at least one disengaging bearing, due to tolerances within the entire kinematic train, one cannot ensure that those portions of the disengaging member which act upon the actuating means invariably assume the same axial position relative to those portions of the actuating means which are to be acted upon. This can result in relatively large departures of the disengaging path of the friction clutch or of the extent of actuating movement which is being imparted to the actuating means. At the very least, such a departure can adversely influence the operation of the adjusting device to such an extent that, under certain extreme circumstances, the adjusting device is no longer capable of carrying out its adjusting function. Furthermore, it can happen that, under certain circumstances when the actuating means covers an excessive distance resulting in undesired adjustment, the friction clutch is no longer capable of being properly disengaged or the initial stressing and the position of the biasing spring are altered to such extent that the force which is actually supplied by the biasing spring is not suffice to guarantee an acceptable transmission of torque.
Published German patent application Serial No. 40 92 383 discloses means for automatically adjusting the position of the pressure plate relative to the counterpressure plate in response to wear upon the friction linings of a clutch disc and (if necessary) in response to wear upon certain other parts, such as the friction surfaces of the two plates. The purpose of the automatic adjustment is to ensure that the bias or clamping action of the friction surfaces on the pressure plate and on the counterpressure plate upon the adjacent friction linings of the clutch disc remains unchanged irrespective of the extent of wear of the friction linings and the friction surfaces of the two plates. The German patent application proposes the utilization of a wear compensating system which employs two annular members and is designed in such a way that the annular members can move axially in response to wear of the friction linings. Such axial adjustment of the annular members determines the axial position of the locations(s) of engagement between the diaphragm spring and the pressure plate and thus compensates for wear, at least of the friction linings. Thus, the position of the diaphragm spring should remain unchanged (namely the same as in a new friction clutch) regardless of the extent of wear upon the friction linings.
A drawback of the friction clutch which is disclosed in the aforementioned published German patent application is that the radial distance of the contact points on the diaphragm spring between the two annular members (one of which surrounds the other) is too small. Moreover, the friction clutch of the German patent application does not allow for accurate initial or subsequent adjustment of the pressure plate, partly due to matching tolerances (especially as concerns the thickness of the annular members in the axial direction of the pressure plate) and partly due to progressive wear of the diaphragm spring and its seat in the friction clutch. A pronounced increase of the distance between the inner and outer annular members is not possible because this would greatly reduce the extent of mobility of the pressure plate in response to the engagement or disengagement of the friction clutch, i.e., the distance of the pressure plate from the counterpressure plate in the engaged and disengaged conditions of the friction clutch would be too small. An undue reduction of such distance would affect the operability of the friction clutch, i.e., attempted disengagement of the friction clutch would not result in an interruption of transmission of torque between the pressure plate and the counterpressure plate on the one hand, and the friction linings of the clutch disc on the other hand.
An additional drawback of the friction clutch which is disclosed in the aforementioned German patent application is that the pressure plate (which is normally affixed to the housing of the friction clutch by leaf springs serving to permit axial movements, but to prevent rotation, of the pressure plate relative to the housing and relative to the counterpressure plate) is free to oscillate in the axial direction when the friction clutch is disengaged. This can result in undesirable adjustment of the annular members relative to the pressure plate in a direction toward the diaphragm spring while the pressure plate is in the process of moving axially and away from the diaphragm spring. Upon the next-following engagement of the friction clutch, the diaphragm spring is likely to assume an improper position (namely a position corresponding to a partially disengaged condition of the friction clutch) with the result that the bias of the diaphragm spring upon the pressure plate in the engaged condition of the friction clutch would depart from the bias during preceding engagement. This would prevent full disengagement of the friction clutch when the operator desires to interrupt the transmission of torque between the pressure plate and the counterpressure plate on the one hand, and the clutch disc (i.e., the friction linings) on the other hand.
Additional prior proposals to automatically compensate for wear upon certain parts, particularly upon the friction linings, of friction clutches are disclosed, for example, in published German patent applications Serial Nos. P42 39 291.8, P43 06 505.8, P42 39 289.6, P42 31 131.4, P42 43 567.6 and P43 17 587.2. The disclosures of all of the just enumerated German patent applications are incorporated herein by reference.
The German patent applications which are enumerated in the preceding paragraph disclose automatically self-adjusting friction clutches which are constructed and assembled in such a way that the pressure plate is urged against the adjacent friction linings of the clutch disc with a pronounced force, but the disengaging force remains low. Moreover, the disengaging force should remain constant or nearly constant during the entire useful life of the clutch. Otherwise stated, the disengaging force should remain at least substantially constant prior to any wear upon the friction linings as well as while the friction linings undergo wear which is to be automatically compensated for until the wear upon the friction lining is too pronounced to warrant further compensation so that the friction clutch must be discarded. This is proposed to be accomplished by employing a clutch spring (such as a diaphragm spring) whose characteristic curve is very steep, i.e., which should be capable of abruptly or rapidly reducing its bias upon the pressure plate. During disengagement of the friction clutch, the disengaging force should fluctuate very little or not at all. This, in turn, fails to cause the available distance-to-force progress of the characteristic curve of the clutch spring to always be available so as to ensure a predictable and complete disengagement of the friction clutch with at least some spare distances to be covered in order to compensate for eventual tolerances. The primary reason is believed to be that the characteristic curve of a clutch spring (diaphragm spring) having a steep characteristic curve during disengagement of the clutch includes a pronounced upwardly sloping portion which immediately follows the downwardly sloping portion. This can be seen in the enclosed FIG. 94 wherein the fluctuations of the force of a clutch spring are measured along the abscissa and the distance which is covered by the spring during dissipation of energy is measured along the ordinate. When the clutch employing a diaphragm spring having a characteristic curve of the type shown in FIG. 94 by a solid line is engaged, the distance which is covered by the spring is at least close to 1 mm. The distance is approximately 2 mm when the pressure plate of the clutch starts to move away from contact with the adjacent friction linings, and the characteristic curve exhibits a rather pronounced upward slope when the covered distance approximates or equals 3 mm. That point of the curve which is reached when the covered distance equals or approximates 3 mm corresponds to the required minimal distance to be covered during disengagement of the friction clutch. This does not take into consideration any of those tolerances which invariably develop during disengagement of the clutch, tolerances developing during assembly of the friction clutch, machining tolerances of component parts of the friction clutch, as well as losses of elasticity during the useful life of the clutch. Additional fluctuations of the distance to be covered by the clutch spring develop due to tolerances of the disengaging means so that the required minimum distance to be covered during disengagement of the clutch is normally at least 3.5 mm. As can be seen in FIG. 94, this distance is covered while the bias of the clutch spring is already on the increase, i.e., when the disengaging force is again quite pronounced. If the clutch employs a sensor of the type disclosed in the aforementioned German patent application Serial No. P 43 39 291.8, the adjusting ring of the wear compensating unit is likely to change its angular position and to thus compensate for non-existent wear or to compensate before the friction linings have undergone sufficient additional wear to warrant a renewed compensation.
An additional drawback of many heretofore known proposals to construct, assemble and operate friction clutches which are equipped with automatic wear compensating means is that the bearings, levers and/or other parts which are used to furnish the disengaging force must be designed to transmit large or extremely large disengaging forces. This, in turn, necessitates the provision of large, complex and expensive thrust bearings for the output element of the prime mover (e.g., the crankshaft or the camshaft of a combustion engine in a motor vehicle) in order to ensure that the bearings will withstand those stresses which develop as a result of the application of pronounced disengaging forces.
An object of the invention is to provide a friction clutch which constitutes an improvement over and a further development of friction clutches disclosed in the published German patent applications Serial Nos. 29 16 755 and 35 18 781.
Another object of the invention is to provide a friction clutch with a device or unit which can automatically compensate for wear upon the friction linings of the clutch disc and for wear upon one or more additional parts of the friction clutch in a novel and improved way.
A further object of the invention is to provide a friction clutch wherein undesirable axial oscillations of the pressure plate cannot adversely influence the adjusting action of the compensating device.
An additional object of the invention is to provide a friction clutch with a novel and improved automatic wear compensating device which can stand long periods of rough treatment, for example, when the friction clutch is used in a motor vehicle to transmit torque between a prime mover and a transmission.
Still another object of the invention is to provide a versatile friction clutch which can be put to use in all kinds of motor vehicles and whose reliability remains unchanged during its entire useful life.
A further object of the invention is to provide a simple and inexpensive friction clutch wherein the wear upon the friction linings of the clutch disc and upon certain other parts is compensated for in a novel and improved way, which is compact, and which can be installed in a power train in a simple and inexpensive way.
Another object of the invention is to provide a friction clutch which can be disengaged in response to the exertion of a relatively small force during its entire useful life.
An additional object of the invention is to provide a friction clutch which embodies the above-outlined features and whose useful life is longer than that of heretofore known friction clutches.
Still another object of the invention is to provide a motor vehicle which embodies the above-outlined friction clutch.
A further object of the invention is to provide a novel and improved combination of prime mover, friction clutch and transmission, particularly for use in motor vehicles.
Another object of the invention is to provide a friction clutch with an automatic wear compensating device whose effectiveness remains at least substantially unchanged during the entire useful life of the friction clutch.
An additional object of the invention is to provide a novel and improved method of compensating for wear upon the friction linings of the clutch disc and upon certain other parts in a friction clutch for use in motor vehicles or the like.
Still another object of the invention is to provide the friction clutch with novel and improved means for preventing unintentional compensation for wear upon the friction linings at a time when a compensation is undesirable or detrimental.
A further object of the invention is to provide the above-outlined friction clutch with novel and improved means for automatically changing the position of the pressure plate.
Another object of the invention is to provide a novel and improved diaphragm spring for use in the above-outlined friction clutch.
An additional object of the invention is to provide a novel and improved housing or cover for use in the above-outlined friction clutch.
Still another object of the invention is to provide a novel and improved combination of housing, diaphragm spring, seat for the diaphragm spring and automatic wear compensating device for use in the above-outlined friction clutch.
A further object of the invention is to provide the above-outlined friction clutch with novel and improved means for centering its components relative to the housing.
Another object of the invention is to provide a novel and improved method of preventing vibrations and/or other stray movements of certain parts of a friction clutch from adversely influencing the automatic adjustment to compensate for wear upon the clutch disc.
An additional object of the invention is to provide a friction clutch with a novel and improved system which automatically compensates for wear upon the pressure plates, upon the diaphragm spring, upon the cover or housing and/or upon the clutch disc or clutch plate.
Another object of the invention is to provide a friction clutch wherein the system which compensates for wear upon the friction linings of the clutch disc and, if necessary, for wear upon certain other parts, can be operated in a simple, reliable and highly accurate manner.
A further object of the invention is to provide a simple and compact compensating system which occupies little room in a friction clutch.
An additional object of the invention is to provide a compensating system which can be installed in existing friction clutches.
Still another object of the invention is to provide the compensating system with novel and improved means for preventing excessive adjustments which would result in overcompensation for wear upon the friction linings.
A further object of the invention is to provide a compensating system which comprises a relatively small number of simple parts and whose accuracy and reliability do not diminish during the entire useful life of the friction clutch.
An additional object of the invention is to prolong the useful life of friction clutches, particularly of friction clutches for use in motor vehicles.
Another object of the invention is to provide a friction clutch whose mode of operation is less affected by wear upon its pans than in heretofore known friction clutches.
A further object of the invention is to provide a friction clutch which an be disengaged in response to the application of a relatively small force.
An additional object of the invention is to provide a friction clutch which is constructed and assembled in such a way that the magnitude of the disengaging force need not change, or changes negligibly, irrespective of the wear upon certain component parts of the friction clutch.
Still another object of the invention is to provide a simple, compact and inexpensive friction clutch which embodies the aforediscussed features.
A further object of the invention is to provide a novel and improved method of compensating for wear upon the clutch plate or clutch disc in a friction clutch of the above-outlined character.
Another object of the invention is to provide a novel and improved method of compensating for wear upon the clutch disc and/or certain other component parts of a friction clutch for use in motor vehicles and the like.
An additional object of the invention is to provide the above-outlined friction clutch with a novel and improved system which can automatically compensate for wear upon the friction linings forming part of the clutch disc.
Still another object of the invention is to provide a fiction clutch which exhibits the above-outlined advantages and which can be assembled at a reasonable cost in automatic machines.
A further object of the invention is to provide a novel and improved aggregate which employs the above-outlined friction clutch as well as one or more additional components, such as the part or parts which transmit torque to the input element and/or receive torque from the output element or elements of the friction clutch.
Another object of the invention is to provide a motor vehicle which embodies the above-outlined friction clutch.
An additional object of the invention is to provide a preassembled modular engageable and disengageable aggregate which embodies the above-outlined friction clutch.
Still another object of the invention is to provide a driving unit which can be used in a motor vehicle and embodies the above-outlined friction clutch.
A further object of the invention is to provide a novel and improved diaphragm spring for use in the above-outlined friction clutch.
Another object of the invention is to provide a novel and improved clutch plate or clutch disc for use in the above-outlined friction clutch.
An additional object of the invention is to provide a novel and improved method of installing a diaphragm spring in the housing or cover of the above-outlined friction clutch.
Still another object of the invention is to provide the above-outlined friction clutch with novel and improved means for tiltably mounting the diaphragm spring for the pressure plate in the housing of the friction clutch.
A further object of the invention is to provide a novel and improved connection between the input element of the above-outlined friction clutch and the output element of an internal combustion engine.
Another object of the invention is to provide novel and improved means for biasing the pressure plate in a friction clutch for use in motor vehicles.
An additional object of the invention is to provide a friction clutch whose operation is not affected by wear (even extensive wear) upon the friction linings, pressure plate and/or other parts which are subject to wear when the friction clutch is in use.
Still another object of the invention is to provide a preassembled friction clutch which can be utilized in existing motor vehicles and/or for other purposes as a superior substitute for existing friction clutches.
A further object of the invention is to provide the above-outlined friction clutch with novel and improved means for opposing the bias of the diaphragm spring for the pressure plate.
Another object of the invention is to provide a novel and improved combination of friction clutch and engine for use in a motor vehicle.
A further object of the invention is to provide a friction clutch with a simple and compact wear compensating system.
An additional object of the invention is to provide a self-adjusting friction clutch wherein all automatic adjustments are highly accurate during the initial stage as well as during advanced stages of wear upon the friction linings and/or upon other component parts of the friction clutch.
Still another object of the invention is to provide a wear compensating system which can be utilized with equal or similar advantage in push-type friction clutches and in pull-type friction clutches.
A further object of the invention is to provide a friction clutch with an automatic wear compensating system which is designed to prevent and to practically exclude untimely and/or inaccurate adjustments of one or more parts while compensating for wear upon the friction linings of the clutch disc.
Another object of the invention is provide a friction clutch with a compact and inexpensive wear compensating system which does not or need not contribute to space requirements and/or to the weight of the friction clutch.
An additional object of the invention is to provide a novel and improved method of rapidly and conveniently assembling the components of the aforementioned friction clutch and its wear compensating system.
Still another object of the invention is to provide a power train which embodies a friction clutch of the above-outlined character.
A further object of the invention is to provide a motor vehicle which embodies the aforediscussed friction clutch and its novel and improved wear compensating system.
Another object of the invention is to provide a novel and improved housing, and a novel and improved pressure plate for use in the above-outlined friction clutch.
Still another object of the invention is to provide novel and improved means for opposing the bias of the diaphragm spring in a friction clutch of the above-outlined character.
A further object of the invention is to provide a self-adjusting friction clutch which can be installed in motor vehicles or elsewhere as a superior substitute for heretofore known and used self-adjusting friction clutches.
Another object of the invention is to provide novel and improved method of monitoring the extent of wear upon the friction linings of a clutch disc and, if necessary, upon certain other parts of a friction clutch.
An additional object of the invention is to provide a novel and improved method of preventing untimely adjustments of a friction clutch to compensate for wear upon the friction linings of its clutch disc or clutch plate.
Still another object of the invention is to provide the above-outlined friction clutch with novel and improved means for compensating for undesirable axial shifting of the pressure plate relative to the counterpressure plate, and relative to the housing or cover.
A further object of the invention is to provide a wear compensating system which automatically responds to detectable wear upon the friction surfaces of the pressure plate and counterpressure plate and/or upon the friction linings of the clutch disc.
Another object of the invention is to provide a novel and improved method of taking advantage of the changes of conicity of the diaphragm spring in a self-adjusting friction clutch.
Another object of the invention is to provide a friction clutch wherein the compensation for wear upon the friction linings of the clutch disc and, if necessary, for wear upon certain other component parts of the clutch is carried out in such a way that the disengaging force remains at least substantially constant and relatively small during each and every stage of disengagement of the clutch and by taking into full consideration all such tolerances which would be, or which are, likely to entail a lengthening of the distance to be covered between full engagement and full disengagement of the clutch.
A further object of the invention is to provide a friction clutch which is constructed and assembled in such a way that, in spite of the incorporation of a wear compensating unit, the magnitude of the disengaging force does not undergo an undesirable and excessive increase during the entire disengagement of the clutch.
Another object of the invention is to construct the friction clutch of the type outlined in the two preceding paragraphs in such a way that it can be constructed and assembled at a reasonable cost and that it ensures accurate and automatic compensation for any and all noticeable wear upon the friction linings or upon the friction linings and additional components of the clutch.
An additional object of the invention is to provide a friction clutch which can satisfy the afore-enumerated requirements event though it is assembled of simple and lightweight components.
Still another object of the invention is to provide a friction clutch which can employ simple and lightweight components even though the disengaging means for the clutch need not employ complex and expensive hydraulic and/or pneumatic servomotors, mechanical actuators with over-the-dead-center movements between the foot pedal and the input element of the friction clutch and/or other devices which are to compensate for abrupt increases of the required force during the last stage or stages of disengagement of the clutch.
A further object of the invention is to provide a friction clutch which is constructed and assembled in such a way that one can avoid the application of large disengaging forces to the bearings or other parts which must be actuated to disengage the clutch with attendant pronounced losses of elasticity and excessive friction.
Another object of the invention is to provide a friction clutch or a torque transmitting apparatus embodying a friction clutch whose actuation does not necessitate the utilization of large, strong and expensive axial or thrust bearings for the output element of the prime mover (such as a combustion engine in a motor vehicle) which drives the housing, the pressure plate and other parts of the clutch in actual use.
One feature of the present invention resides in the provision of an engageable and disengageable friction clutch, particularly for motor vehicles. The improved friction clutch comprises a housing which is rotatable about a predetermined axis, a pressure plate, means (such as a set of leaf springs) for non-rotatably connecting the pressure plate to the housing with limited freedom of movement in the direction of the predetermined axis, a rotary counterpressure plate (such as a flywheel) which is adjacent the pressure plate, a torque transmitting clutch disc disposed between the two plates and having friction linings which are subject to wear in response to repeated engagement and disengagement of the friction clutch, and an axially stressed diaphragm spring which is disposed between the housing. The pressure plate to bias the pressure plate against the clutch disc so that the friction linings are clamped between the two plates in engaged condition of the friction clutch. The diaphragm spring is tiltable relative to a seat which is carried by the housing, and the friction clutch further comprises means for automatically compensating for wear at least upon the friction linings (or upon the friction linings and the adjacent portions of the two plates). The compensating means is effective between the housing and the diaphragm spring to shift the seat relative to the housing in the direction of the predetermined axis. The friction clutch also comprises means for operating the compensating means (such operating means can comprise, for example, one or more torsion springs or one or more coil springs) and means (such as a second spring resembling or constituting a diaphragm spring) for applying to the axially stressed diaphragm spring a supporting force in a direction toward the seat.
The axially stressed diaphragm spring can have a degressive characteristic curve within its operating range. Furthermore, it is often desirable or advantageous that the diaphragm spring be merely force-lockingly propped against the action of the supporting force.
The supporting force and the bias of the axially stressed diaphragm spring can be related to each other in such a way thatxe2x80x94in a contemplated built-in condition of the diaphragm spring, in the absence of changes of conicity of the diaphragm spring due to wear, and within the disengagement range of the diaphragm springxe2x80x94the supporting force is greater than the bias which is applied by the diaphragm spring and opposes the supporting force whereas, when the conicity of the diaphragm spring changes as a result of wear, the supporting force is smaller than the bias which is applied by the diaphragm spring to oppose the supporting force within portions of the path of disengagement of the diaphragm spring.
The means for applying the supporting force can include at least one energy storing device (such as a spring) which changes its shape as a result of wear induced adjustment of the diaphragm spring and/or the seat.
The compensating means can be disposed between the diaphragm spring and the housing (as seen in the direction of the predetermined axis).
The compensating means can comprise sloping surfaces. In accordance with a presently preferred embodiment, the compensating means comprises ramps and the sloping surfaces are provided on the ramps.
As mentioned above, the means for applying the supporting force can comprise an element which resembles (or constitutes) a diaphragm spring. For example, the means for applying the supporting force can comprise a second diaphragm spring which engages the axially stressed diaphragm spring at a predetermined radial distance from the predetermined axis. The arrangement is preferably such that the axially stressed diaphragm spring is tiltable relative to the seat at or close to the predetermined radial distance from the predetermined axis.
The seat can comprise a first portion (e.g., a first wire ring) between the axially stressed diaphragm spring and the housing, and a second portion (e.g., a second wire ring) between the diaphragm spring and the means for applying the supporting force. The second portion of the seat can be disposed between the diaphragm spring and the pressure plate, and the means for applying the supporting force can include means for urging the second portion of the seat against the diaphragm spring. The second portion of the seat can be mounted for movement in the direction of the predetermined axis and the bias of the axially stressed diaphragm spring varies in response to such movement of the second portion of the seat. The bias of the axially stressed diaphragm spring can decrease in response to movement of the second portion of the seat toward the pressure plate. The second portion of the seat can be moved to a position in which the supporting force which is applied thereto is in a state of at least substantial equilibrium with the disengaging force which is applied thereto by the axially stressed diaphragm spring. The aforementioned urging means can comprise energy storing means which applies to the second portion of the seat a substantially constant force within the contemplated adjustment range.
The means for applying the supporting force can include energy storing means which acts as a sensor.
The seat can comprise a first portion which is disposed between the axially stressed diaphragm spring and the housing and is movable in the direction of the predetermined axis toward the pressure plate but is adapted to be arrested against movement in the direction of the predetermined axis away from the pressure plate. Such seat further comprises a second portion which is disposed between the axially stressed diaphragm spring and the pressure plate, and is biased toward the axially stressed diaphragm spring.
The means for operating the compensating means can comprise a spring. The compensating means can comprise a coherent annular adjusting member which is stressed by the axially stressed diaphragm spring in the direction of the predetermined axis in the engaged condition of the friction clutch.
The compensating means can comprise adjustable ramps which slope in the direction of the predetermined axis. The compensating means can further comprise the aforementioned annular adjusting member and the ramps can include a set of ramps which are provided on the adjusting member. At least a portion of the seat can be carried by the adjusting member of the compensating means. The ramps can further include a second set of ramps which cooperate with the (first) set of ramps on the adjusting member. The compensating means can also comprise an annulus between the housing and the adjusting member, and the ramps of the second set can be provided on the annulus. Alternatively, the ramps of the second set can be of one piece with the housing, i.e., the annulus can be dispensed with or a portion of the housing can be said to constitute a functional equivalent of such annulus.
The compensating means can be designed to act as a freewheel in the direction of disengagement of the friction clutch and to be self-locking in a direction counter to the direction of disengagement of the friction clutch.
As already mentioned above, the compensating means can comprise sets of cooperating ramps; the arrangement can be such that the ramps of at least one of such sets are inclined at an angle of 4-20 degrees (preferably at an angle of 5-12 degrees) with reference to a plane which is normal to the predetermined axis.
In accordance with a presently preferred embodiment, the compensating means comprises a first annular member (such as the aforementioned adjusting member) having a first set of ramps, and a second annular member (such as the aforementioned annulus) having a second set of ramps which engage the ramps of the first set and have a slope such that the two sets of ramps are in self-locking frictional engagement with each other. At least one of the two members is movable relative to the other member and is biased relative to the other member in the aforementioned direction to shift the seat relative to the housing.
It is also within the purview of the invention to employ compensating means which employ a plurality of discrete mobile adjusting members (e.g., a set of three or more washer-like or button-like adjusting members).
The compensating means can be designed in such a way that it comprises means for shifting the seat as a function of the rotational speed of the housing. For example, the compensating means can be ineffective when the housing is rotated at least at one of a plurality of different speeds. The arrangement may be such that the compensating means is ineffective when the speed of the housing exceeds a predetermined threshold value. The speeds can include an idling speed (e.g., if the counterpressure plate is driven by the engine of a motor vehicle) and speeds below the idling speed. The compensating means can be designed to be effective at and below the idling speed. It is possible to design the compensating means in such a way that it is effective only, or at least, when the rotational speed of the housing is at least close to zero.
If the compensating means comprises a first member which carries a first set of ramps and a second member having a second set of ramps which engage the ramps of the first set, one of the members is preferably movable relative to the housing in a predetermined direction and is biased in such predetermined direction (such as by the aforementioned compensating means). The one member can be biased in the circumferential direction of the rotary housing.
As mentioned above, the means for applying the supporting force can comprise a resilient sensor, and such sensor can include a portion which is remote from the predetermined axis and reacts against the housing. The housing can include portions which support the sensor.
The friction linings can include first and second sets of linings which are engageable by the pressure plate and by the counterpressure plate, respectively, and the clutch disc which includes such sets of friction linings can further include resilient means for biasing the two sets of friction linings away from each other in the direction of the predetermined axis. Alternatively, the clutch disc or the friction clutch can comprise a suitable substitute for the just-mentioned resilient means. The resilient means or its substitute is deformable, with a first force-to-displacement characteristic, in response to the bias of the axially stressed diaphragm spring upon the pressure plate with a second force-to-displacement characteristic which at least approximates the first characteristic.
The force which is required to actuate the axially stressed diaphragm spring in the disengaged condition of the friction clutch, can be in the range of between minus 150 nm and plus 150 nm.
The axially stressed diaphragm spring can be designed to have a force-to-displacement characteristic with a transition from positive to negative upon disengagement of the clutch disc from the counterpressure plate.
Another feature of the invention resides in the provision of a friction clutch which comprises a pressure plate rotatable about a predetermined axis, a rotary counterpressure plate which is coaxial with the pressure plate, a diaphragm spring which serves to bias one of the two plates axially toward the other plate, and a clutch disc which is disposed between the two plates and has first and second sets of friction linings engageable by the pressure plate and by the counterpressure plate, respectively. The clutch disc further comprises resilient means for biasing the two sets of friction linings away from each other in the direction of the predetermined axis. The resilient means is deformable, with a first force-to-displacement characteristic, in response to the bias of the diaphragm spring upon the one plate with a second force-to-displacement characteristic which at least approximates the first characteristic.
Another feature of the present invention resides in the provision of an engageable and disengageable friction clutch, particularly for vehicles, which comprises: (1) a housing or cover rotatable about a predetermined axis; (2) a pressure plate; (3) means (such as an arrangement of leaf springs) for non-rotatably connecting the pressure plate to the housing with limited freedom of movement in the direction of the predetermined axis; (4) a rotary counterpressure plate (such as a flywheel) adjacent the pressure plate; (5) a torque transmitting clutch disc disposed between the two plates and having friction linings engageable by and disengageable from at least one of the plates, and being subject to wear as a result of repeated engagement with and disengagement from the at least one plate; (6) at least one actuating device and a resilient device disposed between the housing and the pressure plate to bias the pressure plate toward the counterpressure plate and to thereby clamp the friction linings between the plates and to rotate the clutch disc about the predetermined axis in response to rotation of the plates and housing; and (7) means for compensating for wear at least upon the friction linings. The compensating means is disposed between the pressure plate and one of the aforementioned devices and is movable in the direction of the predetermined axis to a position depending upon the extent of wear upon the friction linings. The friction clutch further comprises means for arresting the compensating means in the aforementioned position depending upon the extent of wear upon the friction linings. The arresting means is provided on the pressure plate.
The resilient device can comprise an axially stressed diaphragm spring, and the housing can comprise or carry a ring-shaped seat which tiltably mounts the diaphragm spring. The latter preferably includes an annular portion (which can be called the main portion of the diaphragm spring) engaging the seat, and prongs extending substantially radially inwardly of the annular portion and preferably forming part of the actuating device.
The arresting means can comprise at least one sensor having means for monitoring the extent of wear upon the friction linings, and such monitoring means can comprise a sensor element which is movable relative to the pressure plate into abutment with at least one axially fixed part of the friction clutch (the axially fixed parts include one of the two plates and the housing) to thereby limit the extent of movability of the pressure plate away from the counterpressure plate. The sensor element is preferably movable relative to the pressure plate in the direction of the predetermined axis, and the arresting means preferably further comprises means for automatically coupling the sensor element to an axially movable part of the clutch (the axially movable parts include the diaphragm spring and the pressure plate). The arrangement is, or can be, such that the sensor element comes to a halt upon abutment against the at least one axially fixed part (e.g., one of the plates) of the friction clutch. The at least one axially fixed part can constitute the housing or the counterpressure plate, and the at least one axially movable part can constitute the pressure plate. The sensor element can include a portion which cooperates with a portion of a locating element of the compensating means in response to disengagement of the friction clutch. Such locating element is movable in the direction of the predetermined axis, and the friction clutch preferably further comprises means for movably mounting the locating element on the pressure plate.
Stated in a different way, the compensating means of the improved friction clutch can comprise a locating element for the resilient device, and such compensating means preferably further comprises an equalizing unit which is disposed between the locating element and the pressure plate. The equalizing unit is self-locking in response to engagement of the friction clutch and includes means for automatically adjusting the locating element depending on the extent of wear upon the friction linings in response to disengagement of the friction clutch. The locating element is movable axially of, and away from, the pressure plate and the arresting means can include means for preventing movements of the locating element axially of, and toward, the pressure plate.
The compensating means can be characterized as including a freewheel which is operative during disengagement but is self-locking during engagement of the friction clutch.
In accordance with a presently preferred embodiment, the compensating means of the improved friction clutch can comprise a substantially ring-shaped locating element, and such compensating means further comprises ramps (forming part of the aforementioned equalizing means) which are installed between the locating element and the pressure plate. The ramps can include a first set of ramps which are adjacent the pressure plate and a complementary second set of ramps between the ramps of the first set and the locating element. Such compensating means (or more particularly the equalizing means of such compensating means) can further comprise means (e.g., in the form of coil springs) for biasing the ramps of one set against the ramps of the other set of ramps. The locating element can have a substantially U-shaped cross-sectional outline and can define a substantially annular space (e.g., in the form of an endless groove or channel) for the ramps. Such locating element can contain or can be made of a metallic sheet material, and the ramps can be distributed in the annular space in the circumferential direction of the locating element. The just described compensating means can further comprise means for preventing turning of at least one set of ramps relative to the locating element. Furthermore, the locating element can comprise means (e.g., in the form of ribs and grooves) for axially movably confining at least one set of ramps in the annular space.
The compensating means preferably further comprises wedges, for example, one for each ramp and each carrying the respective ramps. The wedges can be assembled in such a way that they include a first set non-rotatably and axially movably mounted on the locating element and engaging the pressure plate, and a second set between the wedges of the first set and the locating element. The wedges of the second set are movable in the annular space of the locating element relative to the locating element to thereby effect an axial movement of the wedges of the first set and of the locating element relative to each other. Such compensating means can further comprise means (such as pins, studs or other suitable projections and complementary holes, bores, windows or sockets) for preventing rotation of the locating element and the pressure plate relative to each other. Still further, the compensating means can comprise means for biasing each wedge of the second set against a discrete wedge of the first set. Such biasing means can comprise springs (e.g., coil springs) which react against the wedges of the first set and bear against the wedges of the second set. The wedges can be provided with suitable retainers for the respective springs; if the springs are coil springs, the retainers can include studs, plugs or other suitable means for guiding at least the end portions of the respective coil springs.
At least a portion of each wedge of one set is preferably disposed axially of the pressure plate between the locating element and one wedge of the other set.
At least some wedges can contain a heat-resistant and heat-insulating material. For example, at least some of the wedges can contain a heat-resistant material which is selected from the group consisting of thermoplastic and pressure setting (duroplastic) plastic materials.
The wedges of one set can consist of a material having a first coefficient of friction, and the wedges of the other set can consist of a material having a different second coefficient of friction.
The arresting means can include means for limiting the extent of axial movability of the pressure plate away from the counterpressure plate and toward the housing during disengagement of the clutch, and the resilient device (such as the aforementioned diaphragm spring) can include a portion (e.g., a circumferentially complete annular main portion) which bears upon the compensating means in engaged condition of the clutch and is movable axially of the pressure plate to a greater second extent (i.e., to an extent greater than that of the axial movability of the pressure plate away from the counterpressure plate and toward the housing) in response to disengagement of the clutch. The arrangement can be such that the resilient device biases the compensating means only in the engaged condition of the clutch.
The locating element of the compensating means can be designed and positioned to be biased by the resilient device in the engaged condition of the clutch, the wedges of one set can be non-rotatably mounted on the pressure plate, and the locating element and the wedges of the other set can be mounted for rotational movement relative to the pressure plate.
Another feature of the invention resides in the provision of an engageable and disengageable friction clutch, particularly for use in motor vehicles, which comprises a housing or cover rotatable about a predetermined axis (e.g., the axis of the output element of the combustion engine in a motor vehicle), a pressure plate, means (e.g., leaf springs) for non-rotatably connecting the pressure plate to the housing with limited freedom of movement in the direction of the predetermined axis, an axially stressed diaphragm spring between the housing and the pressure plate, an annular seat which tiltably mounts the diaphragm spring in the housing, a counterpressure plate (such as a flywheel) which is rotatable with the housing, and a clutch disc having friction linings between the two plates. The diaphragm spring serves to bias the pressure plate and to thus clamp the friction linings between the two plates in the engaged condition of the clutch, whereby at least the friction linings are subject to wear as a result of repeated engagement and disengagement of the clutch. The clutch further comprises means for compensating for wear at least upon the friction linings. The compensating means is disposed between the pressure plate and the diaphragm spring and includes at least one locating element which is movable in the direction of the predetermined axis and is biased by the spring. The clutch also comprises arresting means including means for limiting and for maintaining at least substantially constant the extent of axial movability of the pressure plate away from the counterpressure plate. The limiting means is disposed between the pressure plate and at least one axially fixed part of the clutch (such as the counterpressure plate or the housing) and includes means for limiting the axial movability of the locating element relative to the pressure plate at least during disengagement of the clutch.
A further feature of the invention resides in the provision of a novel and improved combination of component parts in an engageable and disengageable friction clutch for use in motor vehicles or the like. The combination comprises a pressure plate which is rotatable about and is movable in the direction of a predetermined axis, a diaphragm spring which reacts against an axially fixed part of the clutch to bias the pressure plate axially in engaged condition of the clutch, and arresting means including means for limiting the extent of movability of the pressure plate toward the diaphragm spring in response to disengagement of the clutch. The diaphragm spring includes a portion which at least indirectly bears upon the pressure plate in engaged condition of the clutch and is movable axially of the pressure plate to a greater second extent in response to disengagement of the clutch. The combination further comprises a wear compensating unit between the pressure plate and the diaphragm spring, and such unit is biased by the diaphragm spring only in engaged condition of the clutch.
An additional feature of the present invention resides in the provision of an engageable and disengageable torque transmitting friction clutch which can be utilized with advantage in vehicles, particularly motor vehicles. The improved friction clutch comprises a housing or cover which is rotatable about a predetermined axis, a pressure plate, means (e.g., a group of leaf springs) for non-rotatably connecting the pressure plate to the housing with limited freedom of movement in the direction of the predetermined axis, a rotary counterpressure plate (e.g., a flywheel which is driven by the output element of an engine in a motor vehicle) adjacent the pressure plate, a torque transmitting clutch disc between the two plates, and at least one resilient device reacting against the housing to bias the pressure plate toward the counterpressure plate in order to clamp the clutch disc against the counterpressure plate and to thus rotate the clutch disc about the predetermined axis. The clutch disc has friction linings which are engageable by and disengageable from at least one of the two plates and are subject to wear as a result of repeated engagement with and disengagement from the at least one plate. The friction clutch further comprises an adjusting unit including means for compensating for wear upon the friction linings to thereby maintain the bias of the at least one resilient device upon the pressure plate at a substantially constant value, means for engaging and disengaging the friction clutch including actuating means movable along a predetermined path to engage and disengage the friction clutch, and means for varying the torque transmitted by the friction clutch and/or by the clutch disc, including means for gradually reducing the transmitted torque at least during a portion of movement of the actuating means along the predetermined path to disengage the friction clutch.
The pressure plate comprises a portion which is engaged and biased by the at least one resilient device, and the disengagement of the friction clutch can involve axial movement of the pressure plate away from the counterpressure plate against the bias of the at least one resilient device. The friction clutch can further comprise means for gradually reducing the torque which is transmittable by the friction clutch at least during a portion of axial movement of the pressure plate.
The friction clutch can also comprise means for securing the housing to the counterpressure plate and to thus establish a power train between the actuating means and the securing means. The torque varying means can be disposed in the power train.
The pressure plate has a friction surface which is engageable with the friction linings to establish a power train between the actuating means and the clutch disc, and the torque varying means can be disposed in such power train.
The friction linings can include a first and a second set of friction linings, and the torque varying means can be disposed axially between the two sets of friction linings.
The torque varying means can include means for axially yieldably locating at least one of the two plates and the friction linings relative to the others of the two plates and the friction linings, and the torque varying means can be acted upon by a variable force which decreases to a minimal value in response to disengagement of the friction clutch and gradually increases to a maximum value at least during a portion of movement of the actuating means along the predetermined path to engage the friction clutch.
The means for varying the torque which is transmittable by the friction clutch can include means for reducing the transmitted torque during approximately 40-70 percent of movement of the actuating means along the predetermined path in a direction to disengage the friction clutch and for gradually increasing the torque which is transmittable by the friction clutch during approximately 40-70 percent of movement of the actuating means along the predetermined path in a direction to engage the friction clutch.
The at least one resilient device (such as a diaphragm spring) can have a degressive force-to-displacement ratio at least during a portion of movement of the actuating means along the predetermined path in a direction to disengage the friction clutch.
As mentioned above, the at least one resilient device can comprise a diaphragm spring which bears against the pressure plate. The friction clutch preferably further comprises a seat which tiltably mounts the diaphragm spring in the housing. The diaphragm spring can comprise an annular portion and the actuating means can comprise prongs or tongues which extend from the annular portion of the diaphragm spring. Such prongs can be of one piece with the annular portion of the diaphragm spring. The seat can comprise two portions (e.g., in the form of wire rings) which are disposed at opposite sides of the diaphragm spring. The latter can have a substantially sinusoidal force-to-displacement characteristic curve including a maximum, a minimum, a degressive portion between the minimum and the maximum, an operating point at the degressive portion in the engaged condition of the friction clutch, and a ratio of forces from approximately 1:0.4 to 1:2.7 between the maximum and the minimum.
If the friction clutch is used in a motor vehicle, the means for engaging and disengaging the friction clutch can further comprise means for moving the actuating means and such moving means can include or constitute a pedal which is similar or analogous to the gas pedal of the motor vehicle.
Another feature of the invention resides in the provision of a motor vehicle having a gas pedal, an engageable and disengageable friction clutch, means for engaging and disengaging the friction clutch including actuating means movable along a predetermined path to disengage the clutch, and means for moving the actuating means including a second pedal which is similar or analogous to the gas pedal of the motor vehicle.
An additional feature of the invention resides in the provision of a preassembled engageable and disengageable clutch assembly or aggregate which comprises a housing, a pressure plate, a counterpressure plate which is rotatable about a predetermined axis, means for non-rotatably connecting the pressure plate to the counterpressure plate with limited freedom of movement in the direction of the predetermined axis, a torque transmitting clutch disc between the two plates, at least one resilient device which reacts against the housing to bias the pressure plate toward the counterpressure plate and to thereby clamp the clutch disc between the two plates, friction linings which form part of the clutch disc and are engageable by and disengageable from at least one of the two plates so that they are subject to wear as a result of repeated engagement with and disengagement from the at least one plate, an adjusting unit including means for compensating at least for wear upon the friction linings to thereby maintain the bias of the at least one resilient device upon the pressure plate at a substantially constant value, means for engaging and disengaging the clutch aggregate or assembly including actuating means movable along a predetermined path to disengage the clutch aggregate or assembly, and means for gradually reducing the torque which is transmitted by the clutch disc during a portion of the movement of the actuating means to disengage the clutch assembly or aggregate. The torque reducing means can include at least one resilient element which is in series with the at least one resilient device.
Still another feature of the invention resides in the provision of a clutch aggregate or assembly which comprises a twin-mass flywheel including a first rotary mass connectable to an output shaft of a combustion engine and a second mass rotatable relative to the first mass, an oscillation damper having means for opposing rotation of the two masses relative to each other, and a torque transmitting friction clutch including a counterpressure plate forming part of the second mass, a pressure plate, means for non-rotatably connecting the pressure plate to the counterpressure plate with limited freedom of axial movement, a torque transmitting clutch disc between the two plates, at least one resilient device acting upon the pressure plate to bias the clutch disc against the counterpressure plate, friction linings forming part of the clutch disc and being engageable with and disengageable from at least one of the two plates and being subject to wear as a result of repeated engagement with and disengagement from the at least one plate, an adjusting unit including means for compensating at least for wear upon the friction linings to thereby maintain the bias of the at least one resilient device upon the pressure plate at a substantially constant value, means for engaging and disengaging the friction clutch including actuating means movable along a predetermined path to disengage the friction clutch, and means for gradually reducing the torque which can be transmitted by the friction clutch and/or by its clutch disc during a portion of the movement of the actuating means in a direction to disengage the friction clutch.
The friction clutch of the just-outlined clutch aggregate or assembly can further comprise a housing and means for securing the housing to the second mass so that the housing is separable from the second mass only in response to at least partial destruction or deformation of one of the two parts including the housing and the second mass.
The clutch disc of the aforementioned clutch aggregate or assembly can be provided with at least one substantially annular friction surface and the damper can be located radially outwardly of the friction surface.
A further feature of the invention resides in the provision of a clutch aggregate or assembly for use with a combustion engine, particularly in a motor vehicle. Such clutch aggregate or assembly comprises a torque transmitting friction clutch including a pressure plate, a counterpressure plate (such as a flywheel) which is rotatable about a predetermined axis, means for non-rotatably connecting the pressure plate to the counterpressure plate with limited freedom of axial movement, a torque transmitting clutch disc between the two plates, at least one resilient device acting upon the pressure plate to bias the clutch disc against the counterpressure plate, friction linings forming part of the clutch disc and being engageable with and disengageable from at least one of the two plates and being subject to wear as a result of repeated engagement with and disengagement from the at least one plate, an adjusting unit including means for compensating at least for wear upon the friction linings to thereby maintain the bias of the at least one resilient device upon the pressure plate at a substantially constant value during the useful life of the friction clutch, means for engaging and disengaging the friction clutch including actuating means movable along a predetermined path to disengage the friction clutch, means for gradually reducing the torque which can be transmitted by the friction clutch and/or by the clutch disc during a portion of movement of the actuating means in a direction to disengage the friction clutch, and axially elastic means for coupling the friction clutch with an output shaft of the combustion engine. The coupling means has a stiffness or rigidity which is selected in such a way that any axial, turning, wobbling (tilting) and/or flexing vibrations which are induced by the output shaft of the engine and would normally be transmitted to the friction clutch are damped and/or otherwise suppressed by the coupling means to an extent which ensures proper operation of the friction clutch, and especially proper operation of the adjusting unit.
The stiffness of the coupling means can be selected in such a way that the force to be applied to the actuating means for disengagement of the friction clutch is taken up by the coupling means without appreciable axial shifting of the clutch aggregate or assembly.
The adjusting unit of the just-discussed aggregate or assembly can comprise resilient means in series with the at least one resilient device. Such aggregate or assembly can further comprise means for damping rotational and/or axial and/or radial vibrations of the counterpressure plate and such damping means is connectable between the output shaft of the engine and the counterpressure plate.
An additional feature of the invention resides in the provision of a driving unit particularly for use in motor vehicles, which comprises an at least partially automatic (i.e., fully automatic or semiautomatic) transmission, an engine, and a torque transmitting friction clutch disposed between the engine and the transmission and being controlled at least in dependency on the operation of the transmission. The friction clutch of such driving unit comprises a pressure plate, a counterpressure plate (such as a flywheel) rotatable about a predetermined axis and connectable to the output shaft of the engine, means for non-rotatably connecting the pressure plate to the counterpressure plate with limited freedom of movement in the direction of the predetermined axis, a torque transmitting clutch disc between the two plates, at least one resilient device acting upon the pressure plate to bias the clutch disc against the counterpressure plate, friction linings forming part of the clutch disc and being engageable with and disengageable from at least one of the two plates and being subject to wear as a result of repeated engagement with and disengagement from the at least one plate, an adjusting unit including means for compensating at least for wear upon the friction linings to thereby maintain the bias of the at least one resilient device upon the pressure plate at a substantially constant value, means for engaging and disengaging the friction clutch including actuating means movable along a predetermined path to engage and disengage the friction clutch, and torque varying means including means for gradually reducing the torque which can be transmitted by the friction clutch and/or by the clutch disc during a portion of movement of the actuating means along the predetermined path in a direction to disengage the friction clutch.
The at least one resilient device (e.g., a diaphragm spring) can have a degressive force-to-displacement ratio, at least during a portion of movement of the actuating means along the predetermined path in a direction to disengage the friction clutch.
The means for varying the torque which can be transmitted by the friction clutch can include means for reducing the transmittable torque during approximately 40-70 percent of movement of the actuating means along the predetermined path in a direction to disengage the friction clutch and for gradually increasing the torque which can be transmitted by the friction clutch during approximately 40-70 percent of movement of the actuating means along the path in a direction to engage the friction clutch.
Certain of the above-enumerated objects are accomplished by the provision of a device which compensates for departures of the axial position of the actuating means from an optimum position or compensates for the departures of those portions of the actuating means relative to the disengaging member or disengaging means from an optimum position which are acted upon by the actuating means. Such a device can be utilized with particular advantage in clutch assemblies wherein, in accordance with a further development of the invention, the actuating means is shifted in the axial direction of the disengaging movement in dependency at least upon the extent of wear upon the friction linings because this ensures a practically tolerance-free transmission of force between the disengaging member or the disengaging means and the actuating means. In addition, this ensures that the actuating means can always be moved through the same distance. Thus, and for all practical purposes, there is no play between the disengaging member and/or the disengaging means on the one hand, and the actuating means on the other hand.
It can be of particular advantage if the compensating device is disposed or acts axially between the disengaging member and the actuating device. However, it is also possible to install the compensating device at other locations, e.g., so that it operates between the disengaging member and the disengaging means. In accordance with the present invention, it is advantageous to mount the actuator on an axial guide which is mounted on the transmission, e.g., a tubular guide which surrounds the input shaft of the transmission.
It can be advisable, particularly in clutch assemblies with a friction clutch which comprises a housing, e.g., a sheet metal cover, which can be connected to the counterpressure plate and comprises a bottom wall confronting the disengaging member, to install the compensating device or to cause the compensating device to act axially between the actuating means and the bottom wall. Furthermore, it can be of advantage if the biasing spring constitutes a diaphragm spring which operates axially between the clutch housing and the pressure plate and which comprises a resilient ring-shaped main portion and prongs which extend radially inwardly from the main portion and constitute the actuating means.
In order to ensure proper adjustment by the compensating device, it can be of particular advantage if the compensating device automatically or self-actingly ensures the necessary adjustment in the engaged condition of the clutch assembly or friction clutch and self-actingly or automatically blocks the adjustment during actuation of the friction clutch.
The compensating device can comprise a ring-shaped member which also axially abuts the actuating means in the engaged condition of the friction clutch. The ring-shaped member can compensate for the eventually changing distance between the actuating portions of the actuating means and the disengaging member. It can be of advantage for the operation of the compensating device if the latter comprises adjusting ramps or climbing ramps. Such ramps can be provided on the ring-shaped member.
The adjusting ramps can cooperate with cylindrical or substantially spherical rolling bodies in order to carry out the adjustment. However, it can be of particular advantage if the adjusting ramps cooperate with complementary ramps because, by properly selecting the slope angle of the ramps, one can achieve a self-locking action in response to axial stressing of the ramps. The complementary ramps can also be provided on a ring-shaped member.
Furthermore, and in order to achieve a more economical production of the friction clutch, it can be of advantage if at least one part of the compensating device is made of a plastic material. Such plastic parts can be produced by injection molding. Plastics which are particularly suitable are thermoplastic substances, such as for example polyamide.
It is of particular advantage if the members which include the adjusting ramps are movable in the axial direction in response to actuation of the clutch assembly or friction clutch. It can be of additional advantage if the component parts carrying the clamping ramps and the complementary ramps are rotatable relative to each other. One of these members can be mounted in such a way that it cannot rotate relative to the friction clutch, especially relative to the clutch housing.
In accordance with a further inventive concept, the compensating device can be designed in such a way that it operates or adjusts not unlike a freewheelxe2x80x94as seen in the direction of disengagement of the clutch assemblyxe2x80x94but is self-locking in the direction counter to the direction of disengagement. To this end, the climbing ramps and/or the complementary ramps can be designed in such a way that they define in the axial direction a slope angle which is between 5xc2x0 and 20xc2x0, preferably in the range of between 7xc2x0 and 11xc2x0. It is of advantage if the compensating ramps are designed in such a way that there develops a self-locking action in response to frictional engagement. Thus, one should ensure that under all circumstances the adjusting ramps can self-lockingly engage each other so that it is not necessary to provide by additional means in order to avoid an unintentional resetting. However, such means can be provided if necessary.
In order to ensure an optimal operation of the automatic compensating device, it can be of advantage if at least one of the climbing ramps and/or a member which carries the complementary ramps is spring biased in the direction of adjustment. The spring bias can be achieved in an advantageous manner in that the operation of the other springs, such as especially the biasing or diaphragm spring and the spring which acts upon the axially yieldable friction lining, is not affected in any appreciable manner or is not affected at all. A particularly satisfactory design can be achieved in that the members which are provided with the climbing ramps and the complementary ramps are acted upon or stressed in the direction of adjustment by at least one energy storing element, such as a coil spring, which is installed between these members. Due to such stressing, the members are urged in opposite directions, as considered in the axial direction, i.e., the energy storing elements and the adjusting ramps cause the members to move axially and away from each other. In this manner, the compensating device can be stressed without play axially between the actuating portions of the actuating means and the clutch cover and/or the disengaging member in the engaged condition of the clutch.
In accordance with a particularly advantageous further development of the invention, the coupling assembly can comprise an arrangement for limiting the disengaging movement, at least the disengaging movement of the actuating means. To this end, one can provide a stop which limits the extent of movability of the disengaging member and/or of the disengaging means in the disengaging direction. It is of advantage if the stop is provided on a member forming part of the compensating device and being designed to engage the clutch cover upon completion of a predetermined movement in the disengaging direction. However, it is also possible to provide a stop which includes portions forming part of the disengaging member and abutting an axially fixed part upon completion of a predetermined movement in the disengaging direction. Furthermore, it can be of advantage if the disengaging member also comprises an abutment which is effective in the direction of engagement and which can also constitute a stop. In accordance with an advantageous embodiment, the compensating device is designed in such a way that it props the actuating member in the engaged condition of the clutch assembly. An unchanged actuating movement for the clutch assembly can also be ensured in that a member which forms part of or constitutes the compensating device comprises movement limiting portions which are effective in the direction of disengagement as well as in the direction of engagement and cooperate with the stops. It is of advantage if such a member is constituted by that part of the compensating device which is acted upon by the disengaging member, and the movement limiting stops can be provided on the clutch housing or can form part of such housing. However, it is also possible to limit the extent of actuating movement of the clutch assembly by providing suitable abutments on that component part which guides the disengaging member in the axial direction. Such abutments preferably cooperate with a component part which is connected with the non-circulating bearing race of the disengaging member. Furthermore, the extent of disengaging movement in at least one axial direction can be limited also between the rotating bearing race and a component part, such as for example the clutch housing, which rotates with the bearing race.
In accordance with an additional further development of the invention, it can be of particular advantagexe2x80x94especially for minimizing the progress of the disengaging force or the maximum required disengaging forcexe2x80x94by providing means which effects a gradual reduction of torque adapted to be transmitted by the clutch assembly or the clutch disc during disengagement and at least during a portion of the actuating movement of the actuating means. For example, such means for effecting a gradual reduction of torque can be constituted by the so-called friction lining springs which are provided between the friction linings of the clutch disc, which latter can be clamped between the pressure plate and the counterpressure plate.
A particularly advantageous embodiment of the novel friction clutch can be obtained in that the biasing spring, which is preferably constituted by a diaphragm spring, is tiltably supported by the housing between two seatsxe2x80x94of which one confronts the pressure plate and is spring-biased toward the biasing diaphragm springxe2x80x94in such a way that the maximum disengaging force which the biasing spring applies to the spring-biased seat during disengagement of the friction clutch is increased in response to wear upon the friction linings so that it exceeds the opposing force or supporting force acting upon the spring-biased seat. If the transmission of torque between the pressure plate and the clutch housing is effected by leaf spring elements and/or by a so-called spring arrangement between the friction linings, such as are known for example from the published German patent application No. 36 31 863, it is necessary to take into consideration those forces which such springs apply to the biasing spring in order to determine the force which acts upon the spring-biased seat because such forces are superimposed upon each other. In other words, when the friction linings have undergone a certain amount of wear, the temporarily developing increased disengaging force must exceed the resulting force, with reference to the tilting diameter of the diaphragm spring, of the aforementioned forces; this renders it possible to effect an adjustment. It can be of particular advantage if the spring-biased seat is movable in the axial direction. Furthermore, it can be of advantage if the characteristic curve of the biasing diaphragm spring is configurated in such a way that, starting with a structurally defined position of installation in the friction clutch and in response to a dissipation of energy which is determined by the extent of wear upon the friction linings, the force which is to be applied by the biasing diaphragm spring and hence the level of the progress of the disengaging force increases and that, when the deformation and stressing of the biasing diaphragm spring exceed the deformation and stressing upon installation, the maximum force which is to be applied during disengagement of the friction clutch decreases. Due to such mounting and design of the biasing diaphragm spring, one can ensure that, in response to wear upon the friction linings, there invariably develops again and again a state of equilibrium between the maximum disengaging force of the friction clutch and the opposing force which acts upon the spring-biased seat or the resultant opposing force acting upon the biasing diaphragm spring in the region of the tilting diameter of the biasing diaphragm spring.
It is of advantage if the clutch assembly or the friction clutch is constructed in such a way that the axially movable spring-biased seat is shifted jointly with the pressure plate within the permissible range of wear upon the parts of the friction clutch. The spring-biased seat can be shifted to a small extent in a direction toward the pressure platexe2x80x94during the life span of the friction clutchxe2x80x94in response to gradual or small stepwise adjustment by the adjusting device. Such shifting of the spring-biased seat renders it possible to ensure that the diaphragm spring, which then bears upon the pressure plate, undergoes additional deformation so that the force which is being applied by the diaphragm spring decreases, in a manner as described hereinbefore, until the opposing force or the aforementioned resultant force acting upon the spring-biased seat is in a state of equilibrium with the disengaging force. Thus, the maximum disengaging force of the clutch or by the biasing diaphragm spring is reduced in response to shifting of the spring-biased seat.
It can be of particular advantage if the biasing diaphragm spring is installed in the friction clutch in such a way that its characteristic curve slopes downwardly at least during a portion of disengagement of the clutch, preferably during each and every stage of disengagement. The position of the freshly installed biasing spring can be such that. When the friction clutch is disengaged, the biasing spring reaches, at least substantially, the minimum or the lowermost point of its sinusoidal force-distance progress.
It is of advantage if the opposing force which acts upon the spring-biased seat is furnished by an energy storing element which applies a substantially constant force, at least within the contemplated range of compensation. A suitably designed diaphragm spring which is installed in the friction clutch in a stressed condition is particularly suitable for the application of the opposing force to the spring-biased seat.
The invention is not limited only to the aforedescribed friction clutches but can be put to use generally in friction clutches or clutch assemblies employing an adjusting device which compensates for wear upon the friction linings of the clutch disc.
The invention further relates to a friction clutch, particularly for motor vehicles, having a pressure plate which is connected with a housing in such a way that it cannot rotate but can perform limited axial movements relative to the housing, a biasing diaphragm spring being mounted in axially stressed condition between the housing and the pressure plate so that it can be tilted relative to a seat arrangement which is carried by the housing and that it bears upon the pressure plate in a direction toward a clutch disc which can be clamped between the pressure plate and a counterpressure plate, such as a flywheel, and an adjusting device being provided to compensate for wear upon the friction linings of the clutch disc.
Automatic adjusting devices which are to effect a substantially unchanged biasing of the pressure plate by the biasing diaphragm spring are disclosed, for example, in published German patent applications Nos. 29 16 755 and 35 18 781. The adjusting devices, which are actuatable in dependency upon signals from at least one sensor, are installed or operate between the pressure plate and the biasing diaphragm spring. Due to coupling of the pressure plate with the housing by means of tangentially arranged leaf springsxe2x80x94the bias of the leaf springs must be relatively small because it opposes the bias of the diaphragm springxe2x80x94the pressure plate, whose mass is considerable, is free to perform axial reciprocatory movements when the friction clutch is disengaged. In other words, the pressure plate can become disengaged from the diaphragm spring and this not only adversely affects the operation of the clutch but can also affect the safety of the clutch because the adjusting device compensates when the friction clutch is disengaged until the pressure plate reengages the clutch disc. Thus, the clutch cannot become disengaged. Therefore, such adjusting devices failed to gain acceptance and are not in actual use.
An object of the additional invention is to eliminate the aforementioned drawbacks and to provide adjusting devices of the aforediscussed type which can be put to actual use even under less than optimal circumstances, whose construction is simple and whose operation is always safe, and which have a compact design and can be produced at a reasonable cost. Furthermore, the required disengaging forces should be small and should remain small during the entire useful life of the friction clutch. Still further, the useful life of the improved friction clutch should be longer than that of heretofore known adjustable friction clutches.
In accordance with the invention, such objects are accomplished in a friction clutch having a pressure plate which is biased by a diaphragm spring and wherein the diaphragm spring reacts against a component such as a housing and is tiltable relative to a ring-shaped seat arrangement provided in the housing. The friction clutch further comprises an automatic adjusting device which operates between the cover and the diaphragm spring to move that seat of the seat arrangement which is nearer to the housing so that the seat is moved away from the housing by a distance depending upon the wear on friction linings. The adjusting device can be further transported by an advancing device and the biasing spring is acted upon by a supporting force in a direction toward the seat arrangement. Such a supporting force is preferably applied continuously so that the diaphragm spring is braced against the disengaging force only in a force-locking manner, namely by spring bias, rather than by form-lockingly coupled means. The diaphragm spring is installed with a degressive characteristic curve within its operating range in such a way that the supporting force and the bias of the diaphragm spring are related to each other so as to ensure that the supporting force, by taking into consideration the contemplated position of installation of the diaphragm spring without the wear-dependent change of conicity and within the range of movement of the diaphragm spring during disengagement, exceeds the magnitude of the force which is furnished by the diaphragm spring and acts counter to the supporting force. On the other hand, the supporting force is smaller than the force which is applied by the diaphragm spring counter to the supporting force when the conicity of the diaphragm spring changes in response to wear upon the friction linings. The supporting force can be applied by a single spring element or at least substantially by a single spring element or spring element system. The term xe2x80x9csupporting forcexe2x80x9d is intended to embrace the sum of forcesxe2x80x94to the extent that they are detectablexe2x80x94opposing the bias of the diaphragm spring. Thus, such term embraces for example also or only those forces which are supplied by the (torque-transmitting or disengaging) leaf springs, the bias of springs (in unstressed condition) which act upon the friction linings, or their xe2x80x9csubstitutesxe2x80x9d.
The energy storing element which furnishes at least the major part of the supporting force is preferably a spring, e.g., a diaphragm spring, whose configuration changes during adjustment. However, it is equally possible to employ the leaf springs as energy storing elements which supply the supporting force.
A diaphragm spring which applies the supporting force can bear directly upon the biasing diaphragm spring, e.g., at the radial level of the seat which is movable axially and confronts the cover.
It is particularly advantageous if the adjusting device is disposed axially between the diaphragm spring and the cover. In accordance with an especially advantageous proposal, the adjusting device can comprise sloping surfaces, such as ramps.
The invention ensures that the conicity or initial stressing of the diaphragm spring in the engaged condition of the friction clutch remains substantially unchanged during the entire useful life of the friction clutch and that the pressure plate and hence also the clutch disc is acted upon by a substantially constant force independent of the extent of wear upon the friction linings, upon the pressure plate or upon other elements such as the seat which confronts the cover or the pressure plate, upon the diaphragm spring or the friction surface of the flywheel. The novel proposal further ensures that the mass of the pressure plate is not augmented by the mass of the adjusting device. The mass of the pressure plate continues to remain within a range in which it is shielded from the effects of wear upon the plates and in which it is located at a greater distance from the source of friction heat.
A particularly advantageous embodiment of the novel friction clutch can be arrived at in that the biasing diaphragm spring is tiltably supported by the housing between two seatsxe2x80x94one of which confronts the pressure plate and is spring-biased toward the biasing diaphragm springxe2x80x94and in that the force which is furnished by the biasing diaphragm spring during disengagement of the friction clutch and acts upon the spring biased seat increases in response to wear upon the friction linings and then exceeds the opposing force or supporting force which is being applied to the spring-biased seat. The configuration of the characteristic curve of the biasing diaphragm spring is then such that, starting from a structurally defined position of installation of the biasing diaphragm spring in the friction clutch and taking into consideration that the biasing diaphragm spring dissipates energy in a particular direction in response to wear upon the friction linings, the force which is being applied by the biasing diaphragm spring, and hence the required disengaging force, increases during a first stage but decreases in the course of disengagement when the extent of deformation and stress on of the biasing diaphragm spring further depart from the extent of deformation of the biasing diaphragm spring in the position of installation. Such mounting and design of the biasing diaphragm spring ensure that a state of equilibrium between the force which the biasing diaphragm spring applies to the seat during disengagement of the friction clutch and the opposing force acting upon the spring-biased seat is achieved again and again because, if the supporting force is exceeded by the force which the biasing diaphragm spring applies to the seat, the biasing diaphragm spring shifts the sensor spring away from that seat, which faces toward the cover and the adjusting device can be rotated again in response to the application of force by the advancing device. This results in axial shifting of the seat until the force which is being applied by the sensor prevents further rotation and further axial displacement of the seat.
It is particularly advantageous if, as already mentioned above, the biasing diaphragm spring is installed in the friction clutch in such a way that it exhibits a downwardly sloping characteristic curve, at least during a certain portion of the disengagement range, preferably at least substantially within the entire disengagement range of the clutch. The initial position of the biasing diaphragm spring can be selected in such a way that, in the disengaged condition of the friction clutch, the progress of the distance-force curve of the biasing diaphragm spring reaches or moves beyond the minimum or lowermost value.
The opposing force which is being applied to the spring-biased seat can be generated by an energy storing element which applies a substantially constant force at least within the contemplated range of adjustment. A suitably configurated and prestressed diaphragm spring has been found to be particularly suitable for installation in the friction clutch to act upon the spring-biased seat.
The improved adjusting device can be utilized with particular advantage in friction clutches employing a biasing diaphragm spring which comprises radially outer portions bearing against the pressure plate and additional portions located radially inwardly of the radially outer portions and tiltable in the housing between two seats. In such friction clutches, the diaphragm spring can act not unlike a two-armed lever.
However, the invention is not limited to friction clutches with diaphragm springs which are of one piece with disengaging levers in the form of diaphragm spring prongs but can be embodied also in other types of clutches, e.g., clutches wherein the diaphragm spring is actuated by additional levers.
In order to ensure optimal adjustment to compensate for wear or an optimum biasing force for the friction clutch, it can be of particular advantage if the opposing seat at that side of the biasing diaphragm spring which faces away from the spring-biased seat is configurated in such a way that it can be automatically or spontaneously moved axially in a direction toward the pressure plate but can be automatically or spontaneously arrested by a device against movement in the opposite direction. The adjustment of the opposing seat, namely of the seat which confronts the cover, can be effected by employing an energy storing element which urges the opposing seat in a direction toward the pressure plate, i.e., which opposes the bias of the biasing diaphragm spring. Thus, the energy storing element automatically adjusts the position of the opposing seat to compensate for displacement of the spring-biased seat in response to wear upon the friction linings, and this ensures a clearance-free tiltable mounting of the biasing diaphragm spring.
The opposing seat can be moved axially by an adjusting device which is provided between the biasing diaphragm spring and the cover. The adjusting device can comprise a ring-shaped member, i.e., a coherent or one-piece member, which is biased by the biasing diaphragm spring axially, at least in the engaged condition of the friction clutch.
The tiltable seat assembly can be adjusted to compensate for wear upon the friction linings by rotating the ring-shaped member in the course of the clutch disengaging operation whenever it becomes necessary to compensate for wear. To this end, it is particularly advantageous to provide the ring-shaped member of such adjusting device with adjusting ramps which slope in the axial direction. Furthermore, it can be of advantage if the ring-shaped member carries the opposing support or seat, and such seat can constitute a wire ring. This wire ring can be received in a circumferentially extending groove of the ring-shaped member and can be form-lockingly connected thereto. The form-locking connection can constitute a connection which can hold the wire ring by snap action.
In order to carry out an adjustment, the adjusting ramps can cooperate with cylindrical or substantially spherical rolling elements. However, it can be of particular advantage if the adjusting or sloping ramps cooperate with corresponding complementary ramps because, by properly selecting the angle of slope of such ramps, one can achieve a self-locking action in response to axial stressing of the ramps. The opposing ramps can be carried by a ring-shaped member which can be disposed between the member which carries the sloping ramps and the cover. However, a particularly simple construction can be obtained by providing the opposing ramps in the housing. The latter can be accomplished in an especially simple manner if the housing is made of sheet metal because it is possible to stamp the opposing ramps into the housing. The stamped ramps can be provided in radially extending portions of the housing.
In order to ensure the making of the friction clutch at a reasonable cost, it can be of additional advantage if at least a portion of the adjusting device is made of plastic material. Such plastic parts can be made by injection molding. Thermoplastic substances, such as for example polyamide, can be utilized with particular advantage. The utilization of plastic materials is possible because the adjusting device is disposed at a location which is shielded from heat. Furthermore, the relatively low weight of the plastic material brings about a reduction of the mass moment of inertia.
In accordance with a further inventive proposal, the adjusting device can be designed in such a way that it acts not unlike a freewheel, as seen in the direction of disengagement of the friction clutch, but is self-locking in a direction counter to the direction of engagement. To this end, the sloping ramps and/or the opposing ramps can be designed in such a way that their angle of slope in the axial direction is between 4xc2x0 and 20xc2x0, preferably in the range of between 5xc2x0 and 12xc2x0. It is advantageous to design the sloping ramps and/or the opposing ramps in such a way that a self-locking action takes place as a result of frictional engagement. However, it is also possible to achieve or to assist a self-locking action by the establishment of a form-locking connection, for example, by utilizing a set of soft ramps and a set of profiled ramps or by employing two sets of profiled ramps. Such undertakings ensure that it is not necessary to provide additional means for the purpose of avoiding undesirable resetting.
A particularly advantageous and simple adjusting device can be arrived at if the advancing device which acts in the circumferential direction constitutes a spring which is installed in a stressed condition and yieldably bears at least upon a member which carries the sloping ramps and/or upon a member which carries the opposing ramps or opposing surfaces so that the biased member is resiliently urged in the direction of adjustment. It is advantageous to select the spring bias in such a way that it does not interfere, or does not appreciably interfere, with the operation of other springs, especially the actuating diaphragm spring 4 and the spring which biases the axially yieldable seat.
It can be of advantage, for many applications, if the adjusting device comprises a plurality of shiftable adjusting elements, such as for example adjusting wedges or rolling elements which are movable in the radial and/or circumferential direction. Furthermore, it can be of advantage if the operation of the adjusting device is dependent on the RPM. For example, the centrifugal force which acts upon certain elements of the adjusting device can be relied upon to actuate and/or to lock the adjusting device under certain operating conditions of the combustion engine. It is particularly advantageous if the adjusting device can be blocked by means whose operation depends upon centrifugal force developing when a certain RPM is exceeded. For example, a blocking action can take place when the RPM at least approximates the idling RPM or when the RPM is below the idling RPM, so that a compensation for wear takes place only at a low number of revolutions per minute. This exhibits the advantage that one precludes unintentional adjustments such as could take place as a result of vibrations at a high RPM.
A particularly simple and reliable design of the adjusting device can be achieved by resiliently stressing those component parts which are movable relative to the housing and are provided with sloping ramps and/or opposing ramps. If the friction clutch comprises only one component which is movable relative to the housing and is provided with the corresponding ramps or surfaces, the spring bias is applied to such one component. It can be of particular advantage if the spring bias generates a force acting in the circumferential direction.
It can be of additional advantage, as concerns the construction and operation of the friction clutch, if the sensor springxe2x80x94which can constitute a dished spring, such as a diaphragm springxe2x80x94includes a radially inner portion which reacts against an axially fixed component, such as the housing, and radially inner portions acting upon the seat which faces away from the cover. Such seat can be of one piece with the sensor spring so that the sensor spring also constitutes the seat. In order to hold the sensor spring in a stressed condition, the housing can be provided with abutments or stops. Such abutments can include discrete supporting elements which are provided on the housing. However, it can be of advantage if the abutments are of one piece with the housing, e.g., the housing can be provided with stampings or cutouts or deformed portions which axially abut and thus support the sensor spring.
It can be of particular advantage for the operation of the friction clutch, especially to minimize the progress of the disengaging force or the maximum required disengaging force, if the clutch disc which can be clamped between the pressure plate and the counterpressure plate comprises friction linings and so-called friction lining springs between the friction linings. Such springs are disclosed, for example, in the published German patent application No. 36 31 863. If utilized, such friction lining springs can assist in actuation of the friction clutch, especially the disengaging operation. The reason is that, in the engaged condition of the friction clutch, the stressed friction lining springs exert upon the pressure plate a reaction force which opposes the bias of the biasing diaphragm spring and the actuating diaphragm spring upon such pressure plate. During disengagement of the friction clutch, i.e., while the pressure plate moves axially, the pressure plate is initially pushed back by the resiliently stressed friction lining springs simultaneously with a reduction of the bias of the biasing diaphragm spring upon the pressure plate due to the relatively steep downward slope of the characteristic curve of the biasing diaphragm spring during the initial stage of disengagement of the clutch. A reduction of the force which the biasing diaphragm spring applies to the pressure plate entails a reduction of the force which the friction lining springs exert upon the pressure plate. The actual force which is required to disengage the friction clutch equals the difference between the restoring force of the friction lining springs and the biasing force of the biasing diaphragm spring.
When the dissipation of energy by the friction lining springs is completed, namely when the pressure plate is disengaged from the friction linings, i.e., when the pressure plate releases the clutch disc, the required disengaging force is determined primarily by the biasing diaphragm spring. In accordance with a highly advantageous feature, the force-distance characteristic of the friction lining springs and the force-distance characteristic of the biasing diaphragm spring can be related to each other in such a way that, when the pressure plate releases the clutch disc, the force which is required to actuate the biasing diaphragm spring is small. Thus, by properly relating or even equalizing the characteristics of the friction lining springs and of the biasing diaphragm spring until the pressure plate actually releases the clutch disc, only a very small actuating force or, in extreme cases, no actuating force at all is required to act upon the biasing diaphragm spring in order to overcome the remaining power take-off. Furthermore, the characteristics of the biasing diaphragm spring can be selected in such a way that, when the clutch disc is released, the force with which the biasing diaphragm spring thereafter opposes the tilting movement or the force which is required to tilt the diaphragm spring is very small if compared with the biasing force which the biasing diaphragm spring applies in the engaged condition of the friction clutch. It is also possible to select the characteristics in such a way that, when the pressure plate releases the clutch disc, only a very small force, or practically no force at all, is required to actuate the biasing diaphragm spring in order to disengage the friction clutch. Such friction clutches can be designed in such a way that the actuating forces are in the range of between 0 N and 200 N.
In accordance with a further inventive proposal, the friction clutch can be designed in such a way that the axial force which is applied by the biasing diaphragm spring is in the zero range at least substantially simultaneously with the timing of release of the clutch disc by the pressure plate. As the disengaging operation continues, the force which is then applied by the biasing diaphragm spring can become a negative force, i.e., there takes place a reversal of the direction of application of force by the biasing diaphragm spring. This means that, when the friction clutch is fully disengaged, the clutch automatically remains in the disengaged condition and the engaging operation can be initiated only in response to the application of an external force.
The invention further relates to a friction clutch, especially for motor vehicles, with a pressure plate which is non-rotatably connected with a housing for limited axial movement, at least one biasing spring being installed and being adapted to be stressed between the housing and the pressure plate to bias the pressure plate in a direction to clamp a clutch disc between the pressure plate and a counterpressure plate, such as a flywheel.
Such clutches are disclosed, for example, in the published German patent application No. 24 60 963, in German patents Nos. 24 41 141 and 898 531, and in German Auslegeschrift No. 1 267 916.
An additional object of the present invention is to improve the operation and to prolong the useful life of such friction clutches. A more specific object of the invention is to reduce the magnitude of forces which are required to operate such friction clutches and to ensure that the progress of disengaging forces remains at least substantially unchanged during the entire useful life of the friction clutches. Furthermore, the novel friction clutches should be designed to ensure that they can be produced in a particularly simple and economical manner.
In accordance with the invention, this is accomplished by the provision of an adjusting device which automatically compensates for wear upon the friction linings of the clutch disc and which ensures that the biasing spring exerts upon the pressure plate a practically unchanged force. The friction clutch comprises actuating means for engaging and disengaging the clutch as well as a device which effects a gradual reduction of torque which can be transmitted by the friction clutch or by the clutch disc during disengagement of the friction clutch, at least during a portion of the actuating movement of the actuating means and/or of the distance covered by the pressure plate during disengagement of the clutch. Such a design can further ensure a gradual or progressive increase of torque which the friction clutch can transmit during engagement of the friction clutch and during the initial stage of clamping of the friction linings between the pressure plate and the counterpressure plate.
The novel design of the friction clutch ensures that the stressing of the biasing diaphragm spring when the friction clutch is engaged remains practically unchanged during the useful life of the clutch and this, in turn, ensures that the application of force to the pressure plate remains practically unchanged. Furthermore, the additional undertaking which effects a gradual reduction of torque being transmitted by the friction clutch in the course of disengagement ensures that one can achieve a reduction or minimizing of the progress of disengaging force or of the required maximum disengaging force. This is attributed to the fact that the undertaking assists the actuation, especially the disengagement, of the friction clutch. To this end, the undertaking can comprise axially yieldable resilient means which apply a reaction force to the actuating means and/or to the biasing spring and/or to the pressure plate and/or to the counterpressure plate. The reaction force opposes the force which the biasing spring applies to the pressure plate and is in series therewith.
It can be of particular advantage if the novel torque reducing device of the friction clutch is installed in such a way that it effects a gradual reduction of torque which can be transmitted by the friction clutch or by the clutch disc during a portion of the displacement of those parts of the pressure plate which are being acted upon by the biasing spring during disengagement of the friction clutch.
For many applications, the torque reducing device can be installed in the power flow between the tilting bearing for the actuating means or between the biasing spring and the fastening elements, such as threaded fasteners, which secure the housing to the counterpressure plate.
However, it may be desirable if the torque reducing device is installed in the power flow path between the means for pivotably mounting the actuating means or between the biasing spring and the friction surface of the pressure plate. Such an arrangement is proposed, for example, in the published German patent applications Nos. 37 42 354 and 1 450 201.
For additional applications, it may be particularly advantageous to install the device axially between the friction linings which are disposed back-to-back and form part of the clutch disc, namely to employ a device which constitutes the so-called xe2x80x9cfriction lining springsxe2x80x9d, e.g., which constitutes friction lining spring segments. Such devices are known, for example, from the published German patent application No. 36 31 863.
An additional possibility to achieve a progressive increase or reduction of torque is proposed in the published German patent application No. 216 4 297. The flywheel which is disclosed in this patent application comprises two parts and the member which constitutes the counterpressure plate is axially movably supported relative to the member which is connected with the output shaft of the combustion engine.
It can be of particular advantage for the operation and construction of the novel friction clutch if the torque reducing device facilitates a resilient axial yieldability between the parts of the clutch, the device being installed and designed in such a way that, when the clutch is disengaged, the magnitude of the force acting upon the device is reduced to a minimum and the force acting upon the device gradually rises to a maximum value during the closing of the clutch, i.e., during engagement of the clutch, such rise of the force preferably taking place only during a portion of the engaging or closing movement of actuating means or the pressure plate. It can be of particular advantage if the device is designed in such a way that the gradual reduction or the gradual increase of torque which can be transmitted by the friction clutch takes place while the actuating means completes between about 40% and 70% of its actuating path and/or during between 40% and 70% of the maximum axial displacement of the pressure plate. The remaining portion of the corresponding path is necessary to ensure proper interruption of the power flow and to compensate for possibly existing deformations of parts of the clutch, such as particularly the clutch disc, the pressure plate and the counterpressure plate.
In order to minimize the forces which are necessary to actuate the novel friction clutch, it can be of particular advantage if the biasing spring exhibits a degressive force-distance progress, i.e., that the biasing spring exhibits a decreasing progress of force at least within a portion of its compression or deformation path. In this manner, one causes the spring force of the device to oppose the force of the biasing spring during the disengagement of the friction clutch so that the stressing or deformation of the biasing spring is assisted by the spring bias of the device during a portion of disengagement path and, at the same time, the magnitude of the force which is being applied by the biasing spring to the pressure plate or to the friction linings decreases due to the degressive or downwardly sloping force-distance progress of the characteristic curve of the biasing spring. The actual progress of the force which is required to disengage the friction clutch is the difference between the progress of force which is furnished by the device and the progress of the force which is furnished by the biasing spring, it being assumed that no additional superimposed spring actions are present. During disengagement of the pressure plate from the friction linings, i.e., during release of the clutch disc, the necessary remaining progress of the disengaging force, i.e., the required disengaging force, is established primarily by the biasing spring. The force-distance characteristic of the device and the force-distance characteristic of the biasing spring can be related to each other in such a way that the force which is required to actuate the biasing spring after the pressure plate releases the clutch disc is at a relatively low level. Thus, by selecting the spring characteristic or the force characteristic of the device in such a way that it approximates or actually matches the characteristic of the biasing spring, it is possible to ensure that a very small force or, in extreme cases, no force at all is necessary to actuate the biasing spring until the pressure plate releases the clutch disc.
A particularly suitable biasing spring is a diaphragm spring which, on the one hand, can be tilted in a tilting seat assembly carried by the housing and, on the other hand, bears upon the pressure plate. The diaphragm spring can comprise a ring-shaped body and prongs extending radially inwardly from the ring-shaped body and constituting the actuating means. However, it is also possible to employ actuating means constituted by levers, for example, levers which are pivotably mounted on the housing. Furthermore, it is also possible to apply the spring bias to the pressure plate by resorting to other types of springs, for example coil springs, which are mounted in the friction clutch in such a way that the axial force which such springs apply to the pressure plate in the engaged condition of the friction clutch assumes a maximum value and that the magnitude of such force decreases in the course of the disengaging operation. This can be achieved, for example, by mounting coil springs at an angle relative to the rotational axis of the friction clutch.
It can be of particular advantage if the diaphragm spring is tiltably mounted on the housing between two seats to form part of a so-called push-type clutch. In such clutches, the actuating means which disengage the friction clutch are normally acted upon in a direction toward the pressure plate. However, the invention is not limited to push-type clutches but also embraces pull-type clutches wherein the actuating means for disengaging the friction clutch is normally acted upon in a direction away from the pressure plate.
In a particularly advantageous manner, the novel friction clutch can comprise a diaphragm spring which is designed in such a way that it exhibits a sinusoidal force-distance progress and is installed in such a way that, when the friction clutch is engaged, its operating point is disposed in the degressive range of the characteristic curve which follows the first force maximum. It can be of additional considerable advantage if the diaphragm spring exhibits a force ratio of between 1:0.4 to 1:2.7 between the first force maximum and the following minimum.
Furthermore, it can be especially advantageous if the friction clutch is actuatable by a disengaging system which acts upon the actuating means, such as for example the tips of prongs of the diaphragm spring, and the disengaging system can comprise a clutch pedal which is constructed in a manner similar to that of a gas pedal and is installed in the interior of the motor vehicle. Such a design of the clutch pedal can be particularly advantageous because, due to the novel design, the magnitude of the required force or the progress of force which is required to disengage the friction clutch can be brought to a very low level so that a clutch pedal resembling a gas pedal renders it possible to more readily meter the magnitude of the actuating force.
Due to the novel design of a friction clutch and the attendant possibility to reduce the maximum forces to be applied by the biasing spring during the useful life of the friction clutch, it is possible to reduce the dimensions of the parts or to reduce the strength of the parts accordingly which results in a considerable reduction of the cost of making. By reducing the magnitude of the disengaging forces, one also achieves a reduction of friction and elasticity losses in the clutch and in the disengaging system, with attendant substantial improvement of the system including the friction clutch and the disengaging system. Thus, it is possible to design the clutch in an optimum manner with attendant substantial increase of the clutch comfort.
The novel design is suitable for use in friction clutches in general, and especially in those which are proposed, for example, in German patents Nos. 29 16 755 and 29 20 932, published German patent applications Nos. 35 18 781 and 40 92 382, published French patent applications Nos. 2 605 692, 2 606 477, 2 599 5 444 and 2 599 446, British patent No. 1 567 019, U.S. Pat. Nos. 4,924,991, 4,191,285 and 4,057,131 and in Japanese Utility Models Nos. 3-25026, 3-123, 2-124326, 1-163218, 51-126452, 3-19131 and 3-53628.
The utilization of a friction clutch with automatic or self-acting compensation at least for the wear upon the friction liningsxe2x80x94which ensures an at least substantially constant clamping force during the useful life of the friction clutchxe2x80x94is of particular advantage in connection with clutch assemblies wherein the friction clutch, the clutch disc and the counterpressure plate, such as for example a flywheel, constitute an assembly unit or module. In order to reduce the cost, it is of advantage in connection with such an assembly unit if the clutch housing is attached to the counterpressure plate by way of a non-releasable connection, for example, by a welded joint or by a form-locking connection such as can be achieved, for example, as a result of plastic deformation. Owing to the provision of such a connection, it is possible to dispense with the customarily employed connecting means, such as screws. In such assembly units, it is practically impossible to exchange the clutch disc or the friction lining due to excessive wear without destruction of component parts, such as for example the clutch housing. By employing a clutch which is automatically adjusted to compensate for wear, the assembly unit can be designed in such a way that it ensures proper operation during the entire useful life of the vehicle. Thus it is now possible, due to the novel design, to dimension and design that portion of the clutch disc which is to wear away and that portion of the friction clutch or clutch assembly which is needed for satisfactory adjustment in such a way that the useful life of the clutch, and hence also the useful life of the mounting assembly, invariably at least matches the useful life of the vehicle.
In accordance with a further development of the invention, it can be of particular advantage if a friction clutch which is provided with a wear compensating unit is combined with a so-called twin-mass flywheel. The friction clutch can be mounted, with the interposition of a clutch disc, such that one of the flywheel masses is to be connected with a transmission, and the other flywheel mass is connectable with the output shaft of a combustion engine. Twin-mass flywheels which can be employed in combination with the novel friction clutch are disclosed, for example, in published German patent applications Nos. 37 21 712, 37 21 711, 41 17 571, 41 17 582 and 41 17 579. The entire disclosures of the just-enumerated published German patent applications are incorporated by reference in the present application so that the features which are disclosed in the just-enumerated published German patent applications can be combined, in any desired manner, with the features which are disclosed in the present application. It is particularly advantageous if the clutch housing or clutch cover is connected with the corresponding flywheel in a manner such that the connection cannot be terminated without destruction of the connected parts. Several embodiments of such connections are disclosed in the published German patent application No. 41 17 579.
By utilizing a friction clutch having a unit which compensates at least for wear upon the friction linings, it is further possible to optimize the design of the friction clutch, especially of the energy storing element which furnishes the clamping force for the clutch disc. Thus, this energy storing element can be designed in such a way that, for all practical purposes, it merely supplies that clamping force for the clutch disc which is necessary for the transmission of a desired torque. The energy storing element can be constituted by at least one diaphragm spring or by a plurality of coil springs. Furthermore, the utilization of a self-adjusting friction clutch is of advantage in combination with twin-mass flywheels wherein the torsionally elastic damper which is disposed between the two flywheel masses is installed radially outwardly of the clutch disc or radially outwardly of the maximum diameter of the friction surface on the flywheel mass which is connectable to the transmission. In such twin-mass flywheels, the friction diameter of the clutch disc must be smaller than in conventional clutches so that the biasing force must be increased in accordance with the ratio of the median friction radii in order to be capable of transmitting a predetermined torque from the engine. If one were to utilize a conventional clutch, this would necessitate the application of a greater disengaging force. By utilizing a clutch embodying the wear compensating feature with a progressive reduction of the torque which can be transmitted by the clutch disc during disengagement of the clutch, it is now possible to achieve a reduction of the disengaging force to thus avoid an increase of the disengaging force or, by properly designing the friction clutch, to even achieve a reduction of the disengaging force as compared with a conventional clutch.
Thus, the novel design of the friction clutch can ensure that, in spite of a reduction of the diameters of the friction linings and in spite of the thus required larger biasing force, the disengaging force can remain small. Due to the small disengaging force, the roller bearing which permits the two flywheel masses to rotate relative to each other is subjected to less pronounced wear. Furthermore, compensation for wear renders it possible to prolong the useful life of the clutch so that it is no longer necessary to replace parts, particularly the clutch disc, during the useful life of the motor vehicle. Thus, the clutch cover can be fixedly connected to that flywheel mass which is to be connected with the transmission, for example, by riveting or welding. This is of particular advantage when only a limited space, or a limited outline of the clutch bell, is available so that it is not possible to connect the clutch cover with the flywheel at the side of the transmission in a conventional manner by resorting to screws.
If a clutch assembly consisting of a flywheel and a friction clutch with integrated adjusting means for the wear upon the friction linings is affixed to the output shaft of a combustion engine in a conventional manner, the output element of the combustion enginexe2x80x94particularly a crankshaftxe2x80x94transmits to the clutch assembly axial, rotational and wobbling vibrations. In order to ensure that the operation of the clutch unit or of the adjusting means is not adversely affected by such vibrations, and especially to ensure that such vibrations do not initiate an undesirable adjustment to compensate for wear, it is necessary to design the adjusting means by considering inertia forces of all parts which influence the adjusting means. In order to prevent such undesirable side effects which are caused primarily by the axial and wobbling vibrations, and to avoid a higher cost for the design of the adjusting means for compensation of the wear upon the friction linings in order to take into consideration such side effects, it is further proposed in accordance with an additional feature of the invention to practically separate or isolate the clutch unit and its adjusting means from the axial and flexing vibrations which are initiated by the output shaft of the combustion engine. This can be accomplished in that the clutch unit is connectable with the output shaft of the combustion engine by an axially elastic or resiliently yieldable member. The rigidity of this member is selected in such a way that the member reliably suppresses or damps axial and wobbling or flexing vibrations which the output shaft of the combustion engine transmits to the clutch unit at least to such an extent that one ensures a satisfactory operation of the friction clutch and particularly of its adjusting means. Such elastic members are disclosed, for example, in the published German patent application No. 0 385 752 and in the SAE Technical Paper 9 003 91. The disclosures of such publications are also intended to be incorporated herein by reference. By utilizing an elastic member, it is possible to prevent an undesired compensation for wear which is caused by axial vibrations of the pressure plate relative to the clutch coverxe2x80x94especially when the friction clutch is disengagedxe2x80x94induced by vibrations of the flywheel and/or by vibrations of the diaphragm spring. In the absence of an undertaking to at least substantially suppress the aforediscussed vibrations, especially an axially yieldable disc, such vibrations if applied to a clutch assembly or clutch unit could cause a change of adjustment independently of the extent of wear upon the clutch disc so that the biasing force of the diaphragm spring would be adjusted toward the minimum force which, in turn, would prevent the clutch from continuing to transmit a desired torque.
In accordance with a further inventive concept, a friction clutch which is equipped with a self-acting or automatic compensation and especially wherein an automatic compensation effected in accordance with the present invention can be utilized with particular advantage in a driving unit, especially for motor vehicles, which driving unit consists of an automatic or semiautomatic transmission and a friction clutch which is installed between the prime mover, such as a combustion engine, and the transmission and is actuatable in a controlled or regulated manner at least in dependency upon the actuation of the transmission. An automated or fully automatic actuation of a friction clutch was proposed, for example, in the published German patent application No. 40 11 850.9 to which reference may be had regarding the mode of operation and the necessary constituents.
The heretofore known driving units with automatic or semiautomatic transmissions and conventional friction clutches presented serious problems concerning the actuation of the clutch and the design of the actuators which are necessary for such actuation, such as for example cylinder-piston units and/or electric motors. Very strong or large actuators were necessary due to the relatively large disengaging forces which are required for the actuation of conventional clutches. This involves large space requirements, considerable weight and high cost. Moreover, the reaction time of such large actuators is relatively long due to their high mass inertia. Furthermore, if one employs adjusting cylinders, it is necessary to utilize a large volumetric flow of pressurized fluid which, in turn, renders it necessary to employ a relatively large fluid supplying pump in order to ensure the required actuation times for the corresponding friction clutch. In an effort to partially overcome the aforementioned drawbacks, it was proposed for example in the published German patent application No. 33 09 427 to reduce the actuating force for disengagement of the clutch by appropriate compensating springs which are intended to facilitate the utilization of smaller actuators. However, since the disengaging force for conventional clutches fluctuates within a wide range during the useful life of such clutches, namely the disengaging force is relatively small when the conventional clutch is new but increases during the life of the clutch in response to increasing wear upon the friction linings, a compensating spring can effect only a small reduction of the normally required disengaging force. If one takes into consideration all of the tolerances, it is still necessary to select actuators whose output exceeds that needed for a new conventional clutch in spite of the utilization of compensating springs. By utilizing the novel friction clutch having means for compensating for wear upon the friction linings in combination with a driving unit consisting of an engine and an automatic or semiautomatic transmission, it is possible to greatly reduce the disengaging force in comparison with that which is required for disengagement of conventional clutches, and such reduction can be effected directly in the clutch, so that the magnitude of such reduced disengaging force or the progress of the disengaging force remains practically unchanged during the entire useful life of the novel clutch. This brings about important advantages as concerns the design of the actuators because their actuating output can be correspondingly low with attendant corresponding reduction of the forces and/or pressures which are necessary in the entire disengaging system. Consequently, losses developing in the disengaging system as a result of friction or elasticity of the component parts are either eliminated or reduced to a minimum.
Still another feature of the present invention resides in the provision of an engageable and disengageable friction clutch, particularly for use in power trains between the engines and the wheels of motor vehicles. The improved friction clutch comprises a first component including a housing rotatable about a predetermined axis, a second component including a rotary pressure plate, a third component including means (such as a set of leaf springs) for non-rotatably connecting the pressure plate to the housing with limited freedom of movement in the direction of the predetermined axis, a fourth component including a rotary counterpressure plate which is adjacent the pressure plate and can be driven by a prime mover or the like, a fifth component including a torque transmitting clutch disc disposed between the two plates and having friction linings which are subject to wear as a result of repeated engagement with and disengagement from the friction surfaces of the two plates in response to repeated engagement and disengagement of the friction clutch, a sixth component including a normally frustoconical diaphragm spring which is disposed between the housing and the pressure plate to normally bias the pressure plate toward the clutch disc so that the friction linings are clamped between the two plates, a seventh component including means (e.g., a bearing of one or more levers) for engaging and disengaging the friction clutch, and means for automatically compensating for wear at least upon the friction plates and upon the diaphragm spring). The improved wear compensating means comprises two adjustable rings disposed at different radial distances from the predetermined axis and carried by one of the aforementioned components (e.g., by the housing or by the pressure plate) for displacement in the direction of the predetermined axis toward the diaphragm spring (e.g., toward that side of the diaphragm spring which confronts the pressure plate or toward that side of the diaphragm spring which confronts the housing), and means for adjusting the rings. The adjusting means can comprise a displacing device which is turnable (at least in part) about the predetermined axis and means for turning the displacing device (or a portion of the displacing device) about the predetermined axis.
The one component preferably constitutes one of the first and second components, i.e., the two rings can be carried by the housing or by the pressure plate of the improved friction clutch.
The aforementioned displacing device of the adjusting means forming part of the wear compensating means can comprise ramps, e.g., a set of ramps on one of the rings, a complementary second set of ramps on the pressure plate or on the housing, a third set of ramps on the other ring and a complementary fourth set of ramps on the pressure plate or the housing.
The arrangement is preferably such that at least one portion of a plurality of portions forming part of the diaphragm spring and located at different radial distances from the predetermined axis bears against one of the two rings in the engaged condition of the friction clutch to thereby prevent turning of at least a portion of the displacing device, particularly of the two rings and their (first and third) ramps relative to the pressure plate, the housing or the diaphragm spring and the complementary (second and fourth) ramps. The displacing device can include a first displacing unit for the one ring and a second displacing unit for the other ring. The wear compensating means can further comprise a wear detector which arrests the second displacing unit to prevent adjustment of the other ring but permits the second displacing unit to adjust the other ring in the engaged condition of the friction clutch after the friction linings have undergone at least some wear (i.e., an amount of wear which is detectable by and can be compensated for by the wear compensating means). The wear detector (e.g., a leaf spring or a resilient membrane) is operative to prevent adjustment of the other ring during disengagement of the friction clutch. Such wear compensating means can further comprise means (e.g., in the form of radially extending arms on the two rings) for blocking adjustment of the one ring prior to adjustment of the other ring and for permitting adjustment of the one ring upon completed adjustment of the other ring as a result of subsequent disengagement of the friction clutch.
The rings are rotatable (turnable) relative to each other about the axis of the pressure plate, and the means for turning can comprise coil springs and/or other suitable energy storing elements which bias the rings to turn about the axis of the pressure plate by urging the first and third ramps to move relative to the second and fourth ramps, respectively.
The conicity of the diaphragm spring is changed as a function of wear upon the friction linings of the clutch disc. The aforementioned wear detector of the improved wear compensating means prevents adjustment of the rings during disengagement of the friction clutch but permits adjustment of the rings in response to a change of conicity of the diaphragm spring as a result of wear upon the friction linings. The pressure plate is moved by the diaphragm spring through a distance which is commensurate with the extent of wear upon the friction linings.
The wear compensating means can operate between the housing and the diaphragm spring or between the pressure plate and the diaphragm spring. The entire wear compensating means or at least a portion thereof can be installed between the housing and the diaphragm spring or between the diaphragm spring and the pressure plate, as seen in the direction of the axis of the rotation of the pressure plate, counterpressure plate, housing, clutch disc and diaphragm spring.
The rings are movable in the direction of the aforementioned axis in response to engagement and disengagement of the friction clutch if the one component (such component carries the rings) is the pressure plate, i.e., a component which is movable in the direction of its rotational axis toward and away from the counterpressure plate.
The rings do not share the axial movements of the pressure plate during engagement and disengagement of the friction clutch if they are mounted on a component other than the one including the pressure plate, such as the first component including the rotary housing or cover of the friction clutch.
The aforementioned wear detector of the wear compensating means can be designed to include means for preventing adjustment of at least one of the two rings during disengagement of the friction clutch, preferably for preventing adjustment of at least one of the rings with a variable force. The arrangement is preferably such that the variable force increases in response to progressing disengagement of the friction clutch.
As already mentioned above, the rings are preferably rotatable about the axis of the pressure plate, and the displacing device (such as the aforedescribed device including sets of ramps on the rings and sets of complementary ramps on the pressure plate or on the housing) includes means for moving the rings in the direction of the aforementioned axis in response to rotation of the rings by the turning means (e.g., turning means including coil springs at least one of which reacts against the one component and bears against one of the rings and at least one other of which reacts against the one ring and bears against the other ring). The wear detector (this wear detector prevents rotation of at least one of the rings in the engaged condition of the friction clutch) of the wear compensating means in such a friction clutch can comprise at least one section which is resilient in the direction of the rotational axis of the pressure plate to bias the at least one ring and one of the components (such as the sixth component including the diaphragm spring) in the engaged condition of the friction clutch and in the absence of wear or after completion of the compensation for wear upon the friction liningsxe2x80x94with a force which prevents rotation of the at least one ring under the action of the turning means. The at least one section of the wear detector permits the at least one ring to be rotated by the turning means and the corresponding unit of the displacing device in the engaged condition of the friction clutch. The at least one section of the wear detector is designed to at least reduce the aforementioned rotation preventing force depending on the change of conicity of the diaphragm spring in response to wear upon the friction linings. Otherwise stated, the at least one section of the wear detector is designed to at least reduce the aforementioned rotation preventing force depending on the extent of axial movement of the pressure plate in response to wear upon the friction linings. The turning means is further designed to overcome the inertia of the at least one ring to thus rotate the at least one ring about the aforementioned axis when such ring is free to turn in order to compensate for wear upon the friction linings.
The aforementioned at least one section of the wear detector can be made of a resilient material, e.g., sheet metal. For example, the at least one resilient section of the wear detector can include or constitute a leaf spring or a diaphragm spring, and such at least one resilient section is preferably installed in the friction clutch in a prestressed condition, i.e., so that it stores at least some energy.
The wear detector of the improved wear compensating means can be fastened to the diaphragm spring of the sixth component of the improved friction clutch by rivets and/or in another suitable way.
The wear detector can be constructed and mounted in such a way that it includes a first portion disposed at a first radial distance from the rotational axis of the pressure plate and affixed to the diaphragm spring, and a second portion disposed at a different second radial distance from the axis and bearing against one of the rings. Such wear detector can further comprise a third portion which bears against the diaphragm spring. The first portion of the just-outlined wear detector can be resilient, and the second portion of such wear detector can be spaced apart from the housing when the friction clutch is in the engaged condition, but is moved toward the housing by the pressure plate in response to disengagement of the friction clutch.
The wear detector (e.g., a composite wear detector) can be constructed, assembled and installed to prevent adjustment of at least one of the two rings during disengagement of the friction clutch. Such a wear detector can be provided on the at least one ring, and this ring can comprise a plurality of at least substantially coaxial annular sections which are biased (preferably by the wear detector) axially and away from each other. The at least one ring can include an undulate resilient washer or it can comprise two concentric rings with one or more springs between them to bias the concentric rings axially and away from each other to the extent determined by suitable stops, e.g., the heads of rivets or the like.
As already mentioned above, the means for turning the rings of the wear compensating means in order to account for wear upon the friction linings can include one or more springs, e.g., at least one first coil spring which reacts against the one component (carrying the rings) and bears against one of the two rings, and at least one second coil spring which reacts against the one ring and bears against the other ring in order to change the angular position of the other ring relative to the one ring. The springs which bias the two rings of the wear compensating means can be installed to operate in series. The at least one first spring can store more energy than the at least one second spring, i.e., the at least one (first) spring can turn the one ring (upon completed turning of the other ring) against the opposition of the at least one second spring.
The displacing device and the turning means of the improved wear compensating means can be designed to operate in such a way that one of the rings is rotated about the axis of the pressure plate in a predetermined direction ahead of the other ring. The aforementioned arms or other suitable abutments of blocking means on or at the rings ensure that rotation of the other ring is blocked prior to rotation of the one ring. The abutment of the other ring is preferably located behind the abutment of the one ring (as seen in the direction of rotation of the rings to compensate for wear upon the friction linings), and the abutment of the other ring engages the abutment on the one ring prior to rotation of the one ring ahead of the other ring. The extent of angular movement of the one ring is indicative of the extent of wear upon the friction linings, and the other ring is thereupon rotated until arrested by the abutment of the one ring to thus effect a requisite axial displacement of the pressure plate in a direction toward the counterpressure plate and to thereby effect a change of conicity of the diaphragm spring as well as to compensate for wear upon the friction linings.
The diaphragm spring of the sixth component can form part of the wear compensating means. For example, such diaphragm spring can serve as a means for preventing rotation of one of the two rings in the disengaged condition of the friction clutch. Thus, the diaphragm spring of the sixth component of the friction clutch can be used to prevent adjustment of the one ring in the disengaged condition of the friction clutch.
One of the two rings is or can be spaced apart from another of the seven components of the friction clutch (for example, from the diaphragm spring of the sixth component) in the engaged condition of the friction clutch by a distance which is at least reduced in the disengaged condition of the clutch. The one ring or the other component is movable in the direction of the rotational axis of the pressure plate relative to the other component or the one ring.
If the diaphragm spring of the sixth component of the improved friction clutch forms part of the wear compensating means, it can be designed to bias one of the two rings against the housing (provided that the two rings are installed between the housing and the diaphragm spring) in the disengaged condition of the friction clutch. Alternatively, the diaphragm spring can constitute one of two or more means for biasing the one ring against the housing, or the one ring can be biased against the housing by a part other than the diaphragm spring of the sixth component of the friction clutch.
The arrangement can be such that, if at least one of the two rings is installed between the pressure plate and the diaphragm spring, the at least one ring can be biased against the diaphragm spring in the disengaged condition of the friction clutch. It is even possible to mount at least one of the rings between the pressure plate and the diaphragm spring and to cause the at least one ring to bear against the housing in the disengaged condition of the friction clutch.
The construction of the improved friction clutch can be such that the diaphragm spring abuts one of the two rings at a first radial distance from the rotational axis of the pressure plate and that the diaphragm spring abuts one of the first, second, third, fourth and fifth components at a second radial distance from the axis. The difference between the radial distances of the two rings from each other can constitute at least 30 percent of the difference between the first and second radial distances. The design of the friction clutch can be such that the difference between the first and second radial distances at least approximates the difference between the radial distances of the two rings from the axis.
The wear detector of the wear compensating means can be designed and mounted to undergo deformation through a first distance in response to disengagement of the friction clutch, and the pressure plate is movable in response to disengagement of the friction clutch in the direction of its rotational axis through a second distance which at least approximates the first distance.
At least one of the rings can be provided on the housing and the wear detector can include a portion which is movable relative to the diaphragm spring through a distance Sxe2x89xa7SDxc3x97(L2:L1) wherein SD is the distance covered by the pressure plate for disengagement of the friction clutch, L1 is the difference of radial distances of the two rings from the rotational axis of the pressure plate, and L2 is the difference between the radial distance of one of the rings and the radial distance of a location of contact between the diaphragm spring and the pressure plate.
If the friction clutch is a pull-type friction clutch (i.e., if the means for disengaging it includes means for pulling a portion of the diaphragm spring to disengage the clutch) and the rings of the wear compensating means are disposed between the diaphragm spring and the housing, the diaphragm spring can constitute a one-armed lever privotable or tiltable relative to the ring which is more distant from the axis of the pressure plate, at least during a first stage of disengagement of the friction clutch.
Alternatively, a pull-type friction clutch which embodies the present invention can be constructed in such a way that the diaphragm spring constitutes a one-armed lever privotable or tiltable relative to the ring which is more distant from the axis of the pressure plate during disengagement of the friction clutch. The rings of the wear compensating means in such a friction clutch can be located between the pressure plate and the diaphragm spring.
If the friction clutch is a push-type friction clutch (i.e., if the means for engaging and disengaging includes a bearing or other means for pushing a portion of the diaphragm spring during disengagement of the clutch), the diaphragm spring can constitute a two-armed lever which is pivoted relative to the ring located radially inwardly of the other ring, at least during a certain stage of the disengagement of the friction clutch. The rings of the wear compensating means in such a push-type friction clutch are or can be located between the diaphragm spring and the pressure plate.
Alternatively, a push-type friction clutch which embodies the present invention can be constructed in such a way that the two rings of the wear compensating means are located between the housing and the diaphragm spring and the diaphragm spring constitutes or acts not unlike a two-armed lever which is pivoted relative to the radially outer ring of the two rings during a phase of disengagement of the friction clutch.
The complementary ramps of the displacing device in the wear compensating means can be of one piece with the housing; for example, they can be stamped into the end wall of the housing. The housing can be provided with one or more passages, particularly, between neighboring ramps of the second and/or fourth set of ramps, to permit the flow of cool atmospheric air or another coolant which withdraws heat from the pressure plate, from the diaphragm spring, from the sensor, from the wear detector and/or from the friction linings of the clutch disc.
Alternatively, the ramps which are complementary to the ramps on the two rings can be provided directly on the pressure plate. It is also possible to provide the pressure plate with a separately produced attachment which is or which can be of one piece with the complementary ramps, to support the ramps of the two rings. Furthermore, the pressure plate and its attachment can define at least one recess which serves as a channel for the flow of a coolant, preferably at least in part radially of the pressure plate.
A seat for the diaphragm spring of the sixth component of the improved friction clutch can be provided on or installed in or on one of the two rings forming part of the wear compensating means.
If the friction clutch is a push-type clutch, at least a portion of the wear compensating means can be disposed between the diaphragm spring and the housing, and the clutch can further comprise a resilient sensor bearing against one side of the diaphragm spring, namely against that side which faces away from the aforementioned portion of the wear compensating means.
The sensor can be made of a resilient material and can define for the diaphragm spring a fulcrum to permit tilting of the diaphragm spring, at least during a first stage of the disengagement of the friction clutch. The arrangement can be such that a radially outer portion of the diaphragm spring engages one of the two rings upon completion of the first stage of disengagement of the clutch, and the diaphragm spring thereupon pivots relative to the one ring during a second stage of disengagement of the friction clutch. The one ring is that which is disposed radially outwardly of the other ring, i.e., at a greater distance from the rotational axis of the pressure plate.
If the wear compensating means is disposed between the diaphragm spring and the pressure plate, the resilient sensor can be provided with means reacting against the housing or against the pressure plate and with means for bearing against the pressure plate or against the housing.
Another feature of the present invention resides in the provision of an engageable and disengageable friction clutch which can be utilized with advantage in motor vehicles and comprises an axially fixed component (such as a clutch housing or cover) which is rotatable about a predetermined axis, a pressure plate, means (e.g., a set of leaf springs) for non-rotatably connecting the pressure plate to the component with freedom of movement in the direction of the predetermined axis, a rotary counterpressure plate which is adjacent the pressure plate, a torque transmitting clutch disc which is disposed between the two plates and has friction linings which are subject to wear in response to repeated engagement and disengagement of the clutch, a diaphragm spring which is installed between the component and the pressure plate to normally bias the pressure plate toward the clutch disc so that the friction linings are clamped between the two plates, and means for automatically compensating for wear at least upon the friction linings. The compensating means is disposed between the diaphragm spring and the component.
A further feature of the invention resides in the provision of an engageable and disengageable friction clutch which can be utilized with advantage in the power trains of motor vehicles and comprises an axially fixed component (such as the housing or cover of the friction clutch) which is rotatable about a predetermined axis, a pressure plate, means (such as a set of leaf springs) for non-rotatably connecting the pressure plate to the component with freedom of movement in the direction of the predetermined axis, a rotary counterpressure plate which is adjacent the pressure plate, a torque transmitting clutch disc which is disposed between the two plates and has friction linings subject to wear in response to repeated engagement and disengagement of the clutch, a diaphragm spring which is disposed between the component and the pressure plate to normally (such as when the friction clutch is engaged) bias the pressures plate toward the clutch disc so that the friction linings are clamped between the two plates, and means for automatically compensating for wear at least upon the friction linings. The compensating means comprises concentric adjustable first and second rings which are respectively disposed at first and second radial distances from the predetermined axis and are displaceable in the direction of such axis toward the diaphragm spring, and means for adjusting the rings including first and second displacing units having portions turnable about the predetermined axis and means for turning such portions of the displacing units to thereby displace the respective rings in the direction of the predetermined axis toward the diaphragm spring. The latter includes a portion which is disposed at a first radial distance from the predetermined axis and bears upon one of the rings in the engaged condition of the clutch to thus prevent turning of the aforementioned portion of the respective displacing unit (for the one ring). The compensating means of such friction clutch further comprises a wear detector (e.g., a membrane or a diaphragm spring) having a portion which bears upon the other ring at a second radial distance from the predetermined axis to exert a first force sufficient to prevent turning of the aforementioned portion of the respective displacing unit (namely the displacing unit for the other ring) in the absence of wear upon the friction linings, a lesser second force (e.g., zero force) in response to detected wear in the engaged condition of the clutch to thus permit axial displacement of the other ring through a distance commensurate with the extent of initial wear or uncompensated wear upon the friction linings, and with a third force greater than the second force during disengagement of the clutch. Each of the two displacing units can further comprise at least one first ramp provided on the pressure plate or on the component for each of the two rings, and the aforementioned portions of the displacing units can comprise second ramps provided on the rings and abutting the respective first ramps.
An additional feature of the present invention resides in the provision of an engageable and disengageable friction clutch which can be utilized with particular advantage in power trains between the engines and the wheels of motor vehicles and comprises a housing which is rotatable about a predetermined axis, a pressure plate, means (such as a set of leaf springs) for non-rotatably attaching the pressure plate to the housing with limited freedom of movement with limited freedom of movement in the direction of the predetermined axis, a rotary counterpressure plate which is adjacent and coaxial with the pressure plate, a torque transmitting clutch disc which is disposed between the two plates and has friction linings subject to wear in response to repeated engagement and disengagement of the clutch, a diaphragm spring which is installed between the housing and the pressure plate to normally bias the pressure plate toward the clutch disc so that the friction linings are clamped between the two plates, and means for automatically compensating for wear at least upon the friction linings. The compensating means comprises at least two of the following constituents or features:
(a) First and second rings which are disposed at different radial distances from the predetermined axis and are displaceable in the direction of such axis toward the diaphragm spring, and means for adjusting the rings including first and second displacing units (for example, sets of ramps) as well as means for turning portions of the displacing units to thereby displace the respective rings in the direction of the predetermined axis.
(b) The diaphragm spring include portion which is disposed at a given radial distance from the predetermined axis and bears upon one of the rings in the engaged condition of the clutch to thus prevent adjustment of the one ring.
(c) The compensating means comprises a wear detector having a portion bearing upon the other ring at a radial distance from the predetermined axis, other than the given distance, to prevent adjustment of the other ring in the absence of wear upon the friction linings, to permit adjustment of the other ring in response to detection of sufficient wear upon the friction linings with attendant axial displacement of the other ring, and to prevent adjustment of the other ring during disengagement of the clutch.
(d) The compensating means comprises means (e.g., in the form of arms or other abutments on the rings) for blocking adjustment of the one ring except subsequent to adjustment of the other ring and to an extent which is commensurate with (e.g., identical to) adjustment of the other ring.
A further feature of the present invention resides in the provision of a repeatedly engageable and disengageable friction clutch which comprises a rotary counterpressure plate, a pressure plate which is coaxial with and rotatable with the counterpressure plate, and a clutch disc which is coaxial with and has friction linings disposed between the two plates. The pressure plate has a side which faces away from the friction linings of the clutch disc and the clutch further comprises a seat adjacent the aforementioned side of the pressure plate and a diaphragm spring which is tiltably mounted in or on the seat and bears against the pressure plate in the engaged condition of the clutch with a force to maintain the plates in friction engagement with the friction linings. Such friction linings undergo wear as a result of repeated engagement and disengagement of the clutch, and the latter further comprises means for compensating for wear at least upon the friction linings. The pressure plate is movable axially of and away from the counterpressure plate to and beyond a position in which the pressure plate ceases to bear upon the friction linings during disengagement of the clutch, and the clutch further comprises resilient means serving to apply to the diaphragm spring a force during movement of the pressure plate beyond the aforementioned position so that the force of the resilient means at least substantially matches the force of the diaphragm spring.
The friction linings can include at least one first friction lining which is adjacent the pressure plate and at least one second friction lining which is adjacent the counterpressure plate. Such clutch disc can further comprise means (e.g., in the form of resilient segments) for biasing the first and second linings away from each other.
The resilient means can comprise a compensating spring which is integrated into the clutch. For example, the resilient means can comprise at least one diaphragm spring.
The diaphragm spring which bears upon the pressure plate in the engaged condition of the clutch to maintain the friction surfaces of the two plates in frictional engagement with the friction linings of the clutch disc in the engaged condition of the clutch can be selected in such a way that its characteristic distance-to-force curve denotes the magnitude of the bias during different stages of disengagement of the clutch, and the resilient means can include at least one second spring having a second distance-to-force characteristic curve. The two curves include portions which correspond to the bias of the respective springs during movement of the pressure plate beyond the aforementioned position, and such portions of the two curves preferably depart from each other.
The just mentioned portions of the two curves can indicate that the bias of the at least one second spring is counter to the bias of the diaphragm spring during movement of the pressure plate beyond the aforementioned position.
The compensating means can comprise means for moving the seat for the diaphragm spring toward the counterpressure plate through distances corresponding to the extent of wear upon the friction linings.